Need some help fixing random crashes

Hey guys, so I'm having a few problems with my PC, it runs great normally for surfing and whatever but when I try to play a game (usually something heavy hitting like half life or F.E.A.R) then I get totally random lock-ups, my rig is as follows:

AMD Opteron 165 (clocked up a little to 2Ghz)

XFX GeForce 8600 XXX 320Mb

2Gb of Crucial PC3200 RAM

Gigabyte GA-K8NF-9 Socket 939 Mobo

Black Diamond Power Supply 12cm Fan, 500Watt

Windows Vista Business



So the game runs fine for a while then sometimes (usually about 5 to 10 minutes in) the game crashes, the screen gets cleared to random colour (grey, beige, brown or something else) and my sound is stuck on an infinate loop, I have made a video to better explain it here I don't really know whats causing it cause my temps are pretty normal and I'm running the latest geforce drivers, anyone know what could be wrong?

Nah this problem 99% of the time is related to memory/cpu timings on 939 motherboards.

http://forumz.tomshardware.com/gam [...] 97694.html

Same thing here.