I recently built a new pc with a powercolour 4850 PCS+ and I'm getting some blue rectangle artefacts in source engine games, particularly in shadows and it gets worse when running 8x AA. I also find that at certain times complete walls of textures aren't drawn, so it appears as though half the map is missing. I've only got source engined games to test at the minute so I dont know if it's just something specific. I'm running Vista Ultimate x64 and the catalyst drivers 8.11. The card isn't overclocked at all and I doubt it is overheating because the side is off the case. It is completely stable, runs fine for 3 hours in Left 4 Dead with everything on max, I just get these annoying blue squares. Any thoughts?
Test it with FurMark. Gets my 4870 nearly too hot. If you don't get artifacts with that, you know the card is OK. To me it sounds like bad or overheating graphics RAM. Maybe one of the heatsinks are off or something?