Troubleshooting hard locks

[Marcusben]

I put together the following PC a few months ago:

EPoX EP-9NPA+ Ultra
eVGA Geforce 7800GT
OCZ 2GB (2x1) DDR SDRAM DDR 400 (PC 3200)
AMD Athlon 64 X2 3800+ Manchester 1GHz FSB

I get abour 1 hard lock per 4 hours of usage. All instances vary. It may be on the screensaver, it may be in the middle of a ferocious Civ IV battle, or even surfing the web. Not sure what it could be. My BIOS tells me this after typical usage:

CPU Fan @ 3308 RPM; System Fan @ 0 RPM; Power Fan @ 1231 RPM; CPU Temp @ 39C; System Temp @ 32C.

I have used tried 2 different PSUs (Antec 450W SmartPower 2.0 & Antec 500W SmartPower 2.0), so I don't think the PSU is causing it. Thoughts?

 

[AlgaeEater]

Strictly Video Card or Ram. I had the same problem on my EVGA 7800GT... and I didn't realize it until I opened up my case and saw that my fan on the card stop spinning. Actually I just recently RMA'ed for that sole purpose.

In the past I had the same problem with faulty ram. Basically, since a tiny bit of the ram was damaged (faulty) and it was at the "end" of the ram, whenever I fully loaded up the ram (which was mostly during gaming) or when I had a lot of programs opened that were memory hogs (Kinda like printing 100 color pages), the computer would suddenly either lock up, BSOD, or stall for a really long time, give me a weird error, and then restart.