Ok. I tested the memory. I cleaned everything out. I watched the temperatures. I tested DirectX. I made the I'm using the latest of all of my drivers. I pulled the heatsinks off the cpu and gpu and put new thermal compound on them. I added a more powerful power supply. I've done everything but swap the CPU, graphics card, memory and motherboard, and reinstall Windows. Unfortunately, without buying new ones, I have none to swap in and no friends with them. Serves me right for thinking it was time to upgrade to dual core cpu, DDR2 and PCI-express
So, recap. It happens in ALL 3d games, and ONLY in 3d games. Sometimes I can play for a half hour, sometimes 5 minutes. When it happens, the screen will freeze and sound will skip for maybe 5 seconds and then reboot. Sometimes, the sound will actually recover and not reboot (maybe 10-20% of the time). It's happened since I first built the computer. It doesn't seem to matter how CPU or graphics intensive the game is (WoW, LFS, Doom Legacy, Colin McRae, GTR2 all do it, regardless of what resolution graphics and whatnot).
I really don't want to reinstall windows, and I don't want to blindly buy new parts. Maybe I should take it somewhere (which goes against my morals).
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