Yes, actually it is a Saphire. What drivers are you using and how did you stabilize the voltages? The power management doesn't work ( i think) so I use RIVA tuner to underclock and set the fan. Please advice me!! I know for sure it's not overheating cause I check. Also, I played farcry2 (same OC) and never had a problem.
My PSU is thermatake toughpower 500W. My UPS has a utility that measures the power draw of the PC on the plug. I've checked it and it never reaches 400W so it can't be the PSU, right?