Problems like these often occur due to overheating. Unscrew your PC case and make sure all your fans are running like they should. Make sure to check the fan on the net aggregate too (the wee box you plug the power cable into).

My old PC had that problem, and it was overheating. The fans were all working fine, it's just that the hardware was old and on the way out, more sensitive to heat or something? Idk, but if I took the side off the case and pointed a big house fan into it I could get it to run for a little while longer than normal.

Unfortunately I didn't find which piece of hardware was overheating, as I just got an all-new PC. It wasn't hard drive, anyway, as I managed to put that into this PC and it's still working.

I THINK it was the proc, but it coulda easily been the PSU too. But yeah, sucks to be you!

Usually overheating would show some other symptoms such as program crashes, blue screens, and even video artifact. You can double check by looking at the bios temp readings, changing the shutdown temp limit, and checking that all the fans are working, unobstructed, and in the case of the CPU fan, firmly attached to the heatsink/mobo.

If you haven't installed anything recently, I would venture to say that it's the power supply.

Naw, depends on what parts of the computer overheat and how the hardware handles it. Sometimes the memory, graphics card or processor'll start fuckign up and you get program crashes and artifacts. Sometimes it detects it and just plain shuts down before the hardware is damage.