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Computer turns off 3 seconds after turning on

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January 28, 2012 5:04:18 AM

So i just put together my very first build but i'm having a big problem.

I turn it on and it powers up alright, then turns off after 3 seconds.. on one occassion it turned on, turned off 3 seconds later and then turned up again... i turned it off and kept it disconnected just to avoid causing havoc..

please help!!

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January 28, 2012 6:20:51 AM

breadboard it to make sure there are no short circuitings. only put psu, mobo, cpu, heatsink and a stick of ram. report back after that.
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January 28, 2012 6:32:21 AM

Could be anything from an assembly error to a hardware malfunction.

First:
http://www.tomshardware.co.uk/forum/274745-13-step-step...
Maybe you made a basic mistake.

Second:
Work systematically through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

Third (now it is time to get serious):
The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.
http://www.tomshardware.com/forum/261145-31-read-postin...

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire (standby power supply): 5 volts always on. The green wire should also have 5 volts on it. It should go to 0 volts when you press the case power button (this is also a good way to test the power switch and the associated wiring), then back to 5 volts when you release the case power switch. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The green wire should be 5 volts whenever the PSU is plugged in and the PSU switch is on. It will drop to about 0 volts when the case switch is pressed and go back to 5 volts after it is released.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card (unless you have on board graphics available). In that case, remove any card and connect the monitor cable to the motherboard connector.
Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
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January 28, 2012 7:10:24 AM

Oops! Forgot to mention, i had some trouble with installing the mobo to the case.. one of the bottom holders got stuck with a too-large screw and i could remove it. it doesn't appear to be short anything and others are secured properly..
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January 28, 2012 7:47:50 AM

thanks for the answers guys..

i have tried removing everything except psu, cpu, mobo, heat sink, 1 ram stick.. still no luck, does exactly same thing.

tried resetting cmos by removing battery for 3 minutes - nothing..

maybe it's my psu? not enough power? i'm running an antec 520W

i should have mentioned that one of the screws to hold the mobo in place doesn't go in fully - i stupidly put the wrong screw in and now it's stuck.. maybe it's shorting out? but others are secured properly and make fully contact with the metal bits on the mobo..
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January 28, 2012 9:45:01 AM

if you had a problem with a screw being too big then i guess you should start over there.
I can't stress enough that you MUST breadboard your system. Take EVERYTHING out, psu and all, dont use your case at all. place it all on a non-conductive surface like a cartboard and connect them together, fire it up. If you haven't damaged anything then it should work. if that is all good then you must put them back in and use some non-conductive grommets between your mobo and the case since your problem is probably right there. There are these plastic/paper like thin grimmets to put between your case and the mobo. good luck.
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January 28, 2012 10:03:21 AM

After checking what others have recommended, and if the screw isn't related to the problem, check the CPU isn't getting too hot. You could blow cold air onto it with a hair dryer and see if it stays up for longer. This occurred to me before on an ageing cpu/fan. (I bought a more powerful fan and it was ok.)
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January 28, 2012 10:58:42 AM

vx53c said:
if you had a problem with a screw being too big then i guess you should start over there.
I can't stress enough that you MUST breadboard your system. Take EVERYTHING out, psu and all, dont use your case at all. place it all on a non-conductive surface like a cartboard and connect them together, fire it up. If you haven't damaged anything then it should work. if that is all good then you must put them back in and use some non-conductive grommets between your mobo and the case since your problem is probably right there. There are these plastic/paper like thin grimmets to put between your case and the mobo. good luck.



Yup I've tried breadboarding - the CPU fan fires up works for like 3 seconds then turns off.. funny thing is if I leave the power switch on, it will fire up again and again.. problem is it won't stay on =/
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January 28, 2012 10:59:43 AM

a_dude said:
After checking what others have recommended, and if the screw isn't related to the problem, check the CPU isn't getting too hot. You could blow cold air onto it with a hair dryer and see if it stays up for longer. This occurred to me before on an ageing cpu/fan. (I bought a more powerful fan and it was ok.)


could this be possible even though the CPU and cooler and all other parts are *brand* new?
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January 28, 2012 11:36:51 AM

When you applied the thermal paste did you make sure to have a very even thin layer? It kinda sounds like the the cpu is too hot and turning off to avoid destroying it. Maybe re apply some thermal paste.
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January 28, 2012 11:40:56 AM

zooted said:
When you applied the thermal paste did you make sure to have a very even thin layer? It kinda sounds like the the cpu is too hot and turning off to avoid destroying it. Maybe re apply some thermal paste.

The thermal paste came pre-applied and i just stuck it on directly, didn't use too much force and i secured the CPU fan with the posts in place. I just used the stock CPU fan by the way.

And thanks for answering so quickly - greatly appreciated =)
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January 28, 2012 11:42:26 AM

And thanks to everybody for answering so quickly - greatly appreciated =)
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January 28, 2012 11:43:06 AM

What are you computer specs?
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January 28, 2012 11:45:36 AM

happened to me recently
first, take your motherboard and breadboard it.
try re-seating your heatsink and CPU, re-seat and only use one stick of RAM, make sure the clips "click" into the lock position.

edit: forgot to add, the problem with mine was solved by re-seating the CPU and heatsink.
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January 28, 2012 11:54:00 AM

my specs are a i5-2400, 8gb ddr3 1333 ram, antec 520W psu and a HD 6850 GPU.

thanks for the tip on the CPU re-setting.

would this happen even though the paste was pre-applied?


I might ask a professional to do it because i'm (obviously) a noob with computer hardware, this being my first build.. i will see what he/she says and slet you know...

thanks again for the advice - been very helpful :) 
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January 28, 2012 11:59:55 AM

are you using an aftermarket cooler? or the stock intel cooler? I needed to re-seat my CPU because I think my cooler was on too tight, or the CPU might have not been properly seated. the thermal paste doesn't cause problems though you should remember to apply not too little or too much. when you take out the CPU also remember to carefully check the socket pins for any bent/misaligned ones (*DO NOT touch the pins*)
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January 28, 2012 1:18:52 PM

no i'm using the stock cooler. i just attached it to the cpu using the pre-applied thermal past..
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January 28, 2012 1:21:47 PM

could this be a mobo fault? my friend says when it keeps rebooting spontaneously like this - it could be a m-b fault... but i have no idea, might take it to him to have it checked....
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January 28, 2012 1:38:40 PM

more likely to be something not right on the mobo than the mobo itself. although you CANNOT rule out any other component until you've tested them thoroughly one at a time.
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January 28, 2012 1:59:44 PM

yeah it seems like defective mobo to me.
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January 29, 2012 7:03:12 AM

i'm just going to let my friend take a look and if that doesn't work i will take it to the shop.. will let you know how it goes.

thanks so much for the answers :) 
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January 30, 2012 10:25:34 AM

alright so i have just finished testing it with my friends equipment. here are the results:

- Tried putting his PSU to my mobo: didn't work.
- Tried using his RAM in my mobo: didn't work.
- Tried my RAM in his mobo: works fine.
- Tried my PC speaker on his mobo: works fine.
- Tried his PC speaker on my mobo: didn't work.
- Fixed the misplaced standoff: still doesn't work

I noticed that the PC speakers doesn't work at all on my mobo - just makes clicking noises.

Something new: when i took it to my school and used their power cord - everything else was the same. It powered on for longer than 3 seconds - maybe 10 seconds but then shut off again... But I remember I didn't use it at all for the whole night before i took it to my school so it was pretty well-rested.

I believe it's the mobo or CPU but I don't want to be wrong because returning when there is no real fault means I am charged.

So I have a question - if the CPU was faulty, would it work at all? Would the fan start spinning?

Also I have realised my problem is the repeated re-booting.

Any ideas are most appreciated and the answers thus far have been very helpful - thank-you all for your help in this time of crysis =)
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January 30, 2012 11:47:27 AM

Another note:

I have put the open case in front of a stand-fan that sits in front of an airconditioner. I put the airconditioner on high and the fan on high pointing it straight at the CPU - after a few minutes I started it up...

The results ...
1st boot: powered up for about 3 seconds
2nd boot: powered up for 10 seconds and continued (but I stopped in case I burnt the CPU)
3rd boot: powered up for 3 seconds
4th boot: powered up for 3 seconds.


Does this indicate the heat sink is simply not set properly or perhaps the CPU is faulty ( I bought brand new)?
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January 30, 2012 12:54:25 PM

did you try your friend's psu on your machine or yours on his?
if his doesn't work on yours it is time to rma the board. could you also try the cpu? cpu failure is really really unlikely but you can never be sure.
A faulty psu COULD replicate your problems, so would a faulty mobo. Though usually mobos just get bricked and stay there with fans spinning without it doing anything.
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January 30, 2012 12:56:05 PM

wait you mentioned putting his psu to your board to no avail.
99% is it the mobo, 1% it is the cpu
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January 30, 2012 1:37:20 PM

hm.. seems that it is more likely the mobo is faulty.. i might just get a new mobo tomorrow and see what happens.

any ideas why the computer stayed on longer when i had the air-conditioner cooling it down? that's the only thing that is inconsistent with a mobo fault (according to the limited reading i had managed to get done).

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January 31, 2012 5:22:36 PM

re-seated cpu using new thermal paste and all - didn't work..


GOT NEW MOBO! - Worked!!!!

THank-you all so much, and thanks to everybody here at Tom's Hardware have been invaluable sources of much-needed and much-appreciated information

I made my first build - woot woot woot!!!!!
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January 31, 2012 5:38:55 PM

Best answer selected by kdon27.
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January 31, 2012 6:52:29 PM

This topic has been closed by Mousemonkey
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