Failing PSU?

For the last few days i've been having an issue with my PC. I'll come to turn it on for the first time that day, i'll push the button, and the usual huge roaring sound of everything coming to life fills my room. Then a second later the computer just turns off. Complete power failure. But, it isn't complete. Anything plugged into USB ports still goes, but the computer itself just powers off. There'll be a high pitched whining sound coming from the PSU. I can't get the computer to turn back on without pulling the power cable from the PSU for 5 seconds. Afterwards, it's mostly fine. Sometimes the computer will turn back off again after 10 seconds, sometimes the fans will cut out for a few seconds, but it generally seems to be fine after i pull the cable out for a bit.

The question is, what the dickens is going on? The problems seem to have been occuring ever since the middle of the week, when the switch was tripped on the fuseboard controlling all the power plugs in the house after my dad did something stupid with the microwave. Is it a possibility that the idiocy with the microwave caused a sudden powersurge that damaged my PSU, even if it was briefly for a second before all the power went off?

All hail Our Lord Prosimian, may his reign last for the integral from 10 to 13 function 2xdx years!

Sounds like you've made a fair assessment of the problem. If you can obtain a known good PSU through some means and install it, that'd be the best way to test it. I will caution you that power spikes and surges can sometimes damage internal PC components, not just the PSU. Motherboards especially are often the first thing to go if a surge makes it past a PSU. See if you can test this and let us know how it goes.

:balloon2:

And just like that, the computer is dead. It turns on for about 10 secs, and then kaputski. The only thing that remains working is things connected by USB and a single fan, the main fan for the PSU, quite happily whirring away. I had a look at what goes on inside, and the main CPU fan seems to slow down about a second before everything dies. I'm guessing it has something to do with lack of power, and then it just cascades downward to everything else.

Anyway, this is just wonderful. Financially it couldn't have happened at a better time. Thankfully a good friend in America says he'll order me a new PSU, and all i have to do is pay him back $5 a week over paypal. But for now, i'm stuck on the family laptop, a crappy machine if i ever saw one.