I usually have my PC in hibernation mode at night as I have a programmed task that plays a playlist in winamp to wake me up in the morning. I've been recently getting this problem with my PC, I wasn't getting it before.

Basically after it comes out of hibernation in a few seconds my PC loses power like if it was unplugged. Turning it on doesn't work, I need to unplug the cable from the PSU, wait 2 seconds, and plug it back in and then I can turn it back on(my PSU does not have an on/off switch).

Then after booting the same thing happens at around the Windows loading screen or shortly after going into windows.

I do the same, and this problem won't happen at all again, I can even have it on 3 days straight and this doesn't happen, just twice whenever I come out of hibernation. Also occasionally have it hibernating in the afternoon if I'm not home and the same thing happens, so it must have something to do when I've had the PC hibernating?

I thought it was because the power cable I was using was weak/not making good contact so I got another one and it helped somewhat. But these shut offs are very consistent, they never happen at any other time. I've previously had no problems with this PSU at all, had it for about a month, it's a generic 600W that was recommended to me by the store clerk when I bought my agp 7600GT, and was doing mighty fine with no power problems or lockups at all(no lockups now either). I forgot what the ampere rating were but it's definitely a strong PSU as he suggested it to me as a lot of people who bought an 8800GTX were doing pretty good with it, and the sum of all my PC components' power draw is welllll within acceptable numbers.

So this has to do with hibernation mode then? Is there some power-saving option that may have been turned on?