I started having problems with my desktop PC last week. It was getting slow, sometimes hanging or rebooting itself with no apparant pattern. I tried a rebuild with both Windows XP and Ubuntu Linux and had problems with both. The CPU would go to 100% for no particular reason.
I tried re-seating cards and memory, pulling cards out to see if that helped but kept wondering about the hard drives. That particular part of the case was very warm to touch. So I've now removed the Raptor SATA drive that I was using as the Windows system disk and replaced it with a WD Caviar IDE drive. So far everything's looking a lot better.
At the moment the box is running Ubuntu AMD64 Linux. I managed to get both video cards working and all is looking well. But the AMD64 support is still in its infancy. So it's either get VmWare Workstation up and running with XP, rebuild the box on 32 bit Ubuntu which will improve matters but still need VmWare or just go back to running Windows (boo hiss!).