I've got a DIY box (Chronos III) I built almost a year ago. Athlon 64 3000+ (1.8GHz), ATI Radeon X800XL PCIe, 2GB DDR-400, and a total of 460G of HD space across three drives.
Over the last couple of weeks, it's been turning off. No warning, no errors, no memdumps, nothing in the system log. It happens in the middle of the night when the machine is idle, it happens while you're using it under low CPU load, it happens under high CPU load. It's like a narcoleptic - you're having a conversation, and suddenly *off*. So that's fun.
I'm trying to work out the problem; MemTest86 completed 2 passes with no errors. I recently added a USB hub, so I unplugged that - still happens. The PSU is good quality, but there are always bad apples in the bunch, so it's always a possibility. It could be a heat issue as well, though at this point I doubt it.
Anyway, I just hope I've got this resolved by the time I've got NWN2 on this box; that game will probably have me doing one last upgrade (to an X1950 Pro, when they hit shelves) before Wii comes out, at which point I doubt I'll have much left to spend on my PC.
If anybody has any suggestions, post a comment...