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Computer powers on for a second before turning off

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January 8, 2011 9:34:42 PM

I recently built a new computer, and i initially ran into an issue. My power supply, being mounted on the bottom, didnt have along enough atx12v cord when i had my graphics card in. So i just used my computer without my graphics card. I bought an extension cable for it so then it would fit. So i got the cable today, put in my graphics card, plugged in the extension cable, and then went to boot up my computer. The fans started turning, lights came on, then it all stopped.

I tried taking out my ram, unplugging unessential things, i went down to the bare of having just my power cables plugged in, 2gb stick of ram ( with and without the extension ) and a single fan to tell if it was turned on.

i still had the same problem, i hear no beeps or anything, and the motherboard light is on.

My parts

475 watt power supply ( tried different power supply and same thing happened )
3.4 ghz 965 black edition amd phenom II x4
ASUS M4A785-M motherboard
4.5 gb ram
1tb hard drive
a b U Graphics card
January 8, 2011 9:43:23 PM

Symptoms still indicative of weak PSU....assuming GPU extension cable is not miswired or connected incorrectly....

Remove the GPU again?

Maybe 475 watt PSU *should* be enough, but, that assumes that your PSU can handle the initial power on load, which may be too much for it....
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January 8, 2011 9:48:19 PM

mdd1963 said:
Symptoms still indicative of weak PSU....assuming GPU extension cable is not miswired or connected incorrectly....

Remove the GPU again?

Maybe 475 watt PSU *should* be enough, but, that assumes that your PSU can handle the initial power on load, which may be too much for it....


Well the computer worked fine for a good 5 days, never really had any big issues ( my computer shut down once during a game, and the internet turned off twice but i dont think that is helpful o.o )

i had the gpu out when i tested both power supplies, the only thing currently plugged in are the two power cables to the motherboard ( the atx12v and the one with like 20 pings idk the name :o  ) and the cpu fan, just to see if it is turned on ( it will start to rotate but then stop in like a second )
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January 8, 2011 10:35:19 PM

Is the cpu cooler still mounted securely?
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January 8, 2011 11:21:52 PM

cadder said:
Is the cpu cooler still mounted securely?


yes it's 100% secure

Idk if this will help : I will try and power it up, everything turns on, then off, the motherboard light is on, but then to get everything to turn on, even momentarily i have to turn off the power supply for 8 seconds till the mb light goes off, then it will let me start it back up for a second
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a c 144 ) Power supply
a b U Graphics card
January 8, 2011 11:24:56 PM

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.

If not, continue.

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: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

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.

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 9, 2011 12:46:37 AM

Well jsc, i thought i had it fixed, when i put only 1 stick of ram in it booted up, for about 20 seconds, then it just powered down, the monitor didnt work either.

This was with the graphics card in, i tried it again, it stayed powered up about 2 minutes, still no display though, and it powered down again, and now im back to the same old problem ._. /got so excited too lol

any assistance please :3
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December 13, 2012 4:31:34 PM

I also had a similar experience and in my case, it turned out that the mains supply fluctuated so much that the newer motherboards just cannot work properly and the computer stops either before POST or after.

I had to go back to the laptop setup and never dared to build another desktop.

Just to make sure you're not having the same problem, have you tried taking it to a friends place and see if it will boot up?
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!