If not a temperature, power, or driver issue, it indicates a defective GPU or possibly motherboard (since you had a previous 7950 and it died). What, if anything, are you overclocking (CPU, GPU, memory)?
My cpu is overclocked to 3.8 ghz, its a phenom 965 be. its at 1.37 volt. I have one extra PCIe 16x slot to spare, should i try that slot? And what do you think could be faulty on the motherboard?