Computer Turns on Briefly then right back off again

Question

So yesterday I came home from work and went to turn my computer on....it turned on for about 5 seconds then promptly turned right back off again...before I ever saw anything on the screen. I tried again, same result.

After several attempts, I've found that the length at which it turns on differs. After trying multiple times in a row, it only stays on for about 3 seconds. If I let it rest for a bit it sometimes will stay on for up to a minute (though it never boots, the screen stays black the whole time).

I'm not sure what is causing this issue...I built this computer a little more than 2 years ago and this is the first issue I have ever had with it. I did all the usual checks:
-It's not the power switch
-The capacitors on the motherboard all seem to be in working order
-The PSU seems to be fine as it lights up, fan spins, and will sometimes stay on for about a minute period

My hope is that the thermal paste on the cpu has degraded and just needs to be re-applied. Does that seem like a reasonable assumption?

I'm going to tear the thing apart and do a minimum system build when I get home, but any heads up as to what I should be looking for would be much appreciated.

Any thoughts?

Answer 1

It sounds to me like a PSU fault, like it's providing enough power to start the boot process, but when the big electrical draws start to hit, like the disk(s) being spun up, it can't provide that much power and fails. I wouldn't be surprised if you have blown low-ESR aluminum electrolytic capacitors in the PSU.

I just had a wall-wart power supply for a set-top box fail due to this, and using a multimeter I could see it was still putting out the right voltage under no load or light load, but as soon as full load was applied it was failing.

See also: The Capacitor Plague, and BadCaps.net.

Answer 2

I wouldn't have thought that the cpu could get to a cut out temp in 5 seconds or perhaps even in a minute unless there were no cooling at all. Reapplying the thermal paste can't hurt but I don't think it is the solution.

CPU also wouldn't explain nothing being on the screen. More likely is something else is borked on the mobo which breaks as soon as it heats even slightly. I would think something bios related given that it doesn't get into the boot sequence proper.

Answer 3

Check your ram, try resetting it or running with only one stick. The ram I used to have failed after a few months regularily so it is a strong possibility thats what failed. there is usually no output when ram quits as the bios cannot even load. Although when ram fails there are usually signs as it degrades, like random bsod or windows failing to start or come back from standby,

Is the computer overclocked? try resetting the cmos, there may be jumpers.