I have this exact problem as well. This happened to me a couples months ago, but the problem still exists. I RMA'ed my 6950 and got a replacement, switch power supply from an Ultra x4 to Corsair.
-AMD 1090t @3.8ghz
-GSkill 8GB RAM
-Western Digital Caviar Black 750GB
It's such a frustrating problem
. Stressed my GPU, and everything. Looks like it's not gpu.
so...i guess I'll just have to wait for time to tell.