Hardware Failure

OK so my sons PC powered down last night (not shut down, powered down) while playing a game.
Now it wont start up, small whir of the fans and thats it.

I know what I think it is but I would like some ideas to verify.

I've thoroughly cleaned it out and replaced the thermal paste on CPU.

So.... what do you guys think?

 

My first guess would be that the power supply bit the dust.

 

Well that was one of my thoughts but I'm pretty sure it's got power, educated guess, something I can't test for a few days until I get a compatible PSU.

 

I agree it sounds like a power supply issue.

My only tip is not to trust the results from a PSU tester. Since a tester only draws a few watts, it won't measure the PSU's performance under load (the actual wattage draw of the PC). This is similar to a car battery: A multimeter hooked to the terminals may show 12 volts; however the load of the starter results in only "click...click,click".