PC shut downs automatically after 10-20 second. No POST screen, no beeps

Posted by emzero on Super User See other posts from Super User or by emzero
Published on 2012-03-23T02:38:34Z Indexed on 2012/03/24 17:32 UTC
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I have this not-so-old computer that's not being used for a year or so.

Specs:

When I power on the computer, everything seem to start, but right away the whole system shuts down.

I've removed and changed the RAM sticks, take out the VGA, everything I could think of.

So what could it be causing this? The PSU? The motherboard is dead? The CPU? Any help to isolate the problem will be useful.

Thanks

PS: Please don't close the question, this could be helpful to anybody having a similar problem, even with different hardware.

UPDATE

I've removed the old thermal paste and apply a brand new one.
I also cleaned every dust using a high pressure gas dust remover.
Checked for bad capacitors, all of them seem ok.
Opened the PSU, removed big giant dust balls, cleaned with high pressure dust remover.

Still the same problem, but now it stays powered on for almost 20 seconds maybe. But no POST screen, no beeps at all, nothing.

So I suspect it's a motherboard or PSU failure. Unfortunately I don't have an energy tester to test the PSU...

Don't know what else to try. I don't have another 775-motherboard to test the CPU, RAM and VGA with it.

Developer IT