Dude – you’ve got to run Memtest! I’d guess you have a memory error -it’s free, man, why not?
SMART is Self-Monitoring, Analysis and Reporting Technology and allows you to tell if your hard drive is about to fail. It is not infallible, but an extended test can be run for free by several programs. It’s worth checking as failing hard drives can load or save corrupt data and bugger the PC up. Usually you’ll find it just hangs as the drive as the drive fails to read a sector and the PC waits for that ’till you loose patience and restart.
However, sometimes other funny issues pop up with a failing HDD so it’s worth running a test even if only to rule it out.
Try this in Windows. Download and install Speedfan then head over to the SMART tab and run extended tests on your drive(s). I usually also read the report, which is where it sends the test data to a website which gives you a more intelligible interpretation of the jargon returned. If nothing fails, I wouldn’t get worried about it, but it might show up your problem. You can also use it to monitor and graph your various sensor temps*.
It’s the same with Memtest+ – you need to eliminate things at this point.
If it’s neither of these I’d be guessing PSU as next most likely.
*Some mobo temps may be higher than you expect, my EX58 board has the chipset up to 80. Well it did ’till I removed the stupid decorative sticker that covered most it. Thanks Gigabyte, really well thought out. 🙄