It sounds like a power issue to me. Do the voltages looks Ok in the BIOS?

Is the memory Ok? http://www.memtest.org/

In my experience, if it's not the hard drive or the RAM, then a hang failure is more likely to be the power supply than anything else. But I have very limited experience with PC failures so YMMV.

If you need to back the stuff up, this treated me very well when I used it: http://clonezilla-sysresccd.hellug.gr/

HTH. Good luck!

Cheers,
Scott.