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PC Turns on but no POST or beeps (Not a new build)

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Anonymous
a b B Homebuilt system
April 10, 2010 4:13:14 PM

Hi,

Ive had my pc for a couple years now, and has worked fine until now.
Today I was using my pc and it just shut down for no reason. Now when I turn it on, the fans spin, the lights turn on but 3 seconds later it shuts down, then it turns on 2 seconds later by itself. It never Posts, just a blank screen and no beeps.

When I opened the case I smelt something was burning, but could not locate where it was coming from.

I have tried taking it all out the case, and lying it on my desk. Nothing.
Tried taking everything out except PSU, CPU, MOBO and HSF. Nothing, not even beeps to indicate no RAM/GPU.
Tried clearing CMOS. Nothing.

Not sure what else there is to do :(  totally stuck. I'm pretty sure something is probaly gone, but no idea which component. I suspect PSU, but it could just as easily be the Mobo or CPU.

Have no spares to swap with either.

Any help/advice would be greatly appreciated.
Thanks in advance.

More about : turns post beeps build

Anonymous
a b B Homebuilt system
April 10, 2010 4:16:32 PM

Sorry, forgot to add the specs!

Specs:
Mobo: Asus p51-E
CPU: Intel dualcore (conroe) E6600
RAM: Corsair 2gb 1066mhz (2 sticks)
GPU: nVidia Gainward 8600
PSU: Seasonic 600W
April 10, 2010 10:58:53 PM

hookup just a drive to the power supply to see if that keeps running, remove data cables to motherboard. If that works stays on then measure voltage on 24pin connectior with meter, borrow one.
First since you have removed the board, use your nose and sniff around for the burnt component. Then do the same to your power supply, ask someone else to do the same without telling them anything specific. The purpose being to pinpoint where the burnt component is, their opinion is not likely to be clouded.
The power supply is designed with protections to shut itself down when a short or improper voltages are detected, then clear itself for a few seconds and try again. Since most PSU require a load to start this is why I suggest to plug just a drive in, an old one lying around would be best. If the voltages inside the PSU are shuting it down it might duplicat itself this way. If it runs ok and measures good across the 3.3v, 5.0v and 12.0v you can start looking at motherboard or any cards (video).
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a c 122 B Homebuilt system
April 11, 2010 1:19:18 AM

No beeps from a formerly working system means a failure in (most to least likely) PSU, motherboard, or CPU. Practically anything else will generate a failure beep pattern.

You have worked through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
yes?

I mean work through, not just read over it.

Breadboard - that isolates any kind of case problem.
http://www.tomshardware.com/forum/262730-31-breadboardi...
Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

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.

So, the best bet is to replace the PSU with a known good one of similar power capacity. Brand new, out of the box, untested does not count as a known good PSU.

Next best thing is to get (or borrow) a digital multimeter and check the PSU.

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. 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...

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.
Anonymous
a b B Homebuilt system
April 11, 2010 11:05:14 AM

Thank you roonj and jsc for your responses.

roonj: I don't have a voltage meter, I'll ask a friend who might have one, but I doubt he does.
Whilst I'm going round his house to ask for a volt meter, I'll get him to sniff around, but to be honest I think the smell has completely gone by now.
Thanks to jsc's youtube vid, I've tried running the PSU on its own with only a fan and DVD drive. It turns on fine with no shutting down.

jsc: I have worked through as many of the standard checklists as I can. I do not have spare parts, so I cant swap in a GPU, PSU, CPU etc. Have also tried breadboarding.

My mobo has a power and reset switch on it, which helps eliminate the case completely when breadboarding. As mentioned, I get no beeps whatsoever with only the PSU, mobo, CPU and HSF.

I tried that brilliant idea shown in the corsair youtube vid for testing the psu. It seems to run fine in that test.


UPDATE: I've got some extra information that might help pinpoint the issue.
I got an SSD yesterday (the day my computer died). I plugged it into an unused cable thread (you know how many threads come out of the PSU, usually with multiple plugs on a single thread). It was shortly after this that the computer died. I took a closer look at the cable thread used, and the very last plug at the end has the orange wire pulled out of the plug. I've known about this for a while, but it has not caused any problems for the past 2 years. That being said, I left it alone and never plugged anything to it, until today with the SSD.

I'm going to try and test my mobo with a friend's working PSU later today. This should help check to see if it's actually the PSU or not. Will update you when I get back.

Again many thanks for your ideas.
Anonymous
a b B Homebuilt system
April 11, 2010 5:59:56 PM

Just tried it at a friend's. I used his working PSU that he uses in his PC and still got the same problem.

So it's looking like either motherboard or CPU, but have no idea how to find out which one it is without swapping in a spare CPU. My friend wouldnt let me use his :( 
June 18, 2012 6:28:01 AM

i have the exact same problem right now i just cant figure it out
!