From what ive read in the past seem like it was because you had 2 psu hooked up ive seen similar problem. How do have the 2 PSU hooked up? I am sure someone on here can chime in about there experience. I have seen this more then once on this forum.
One psu was for the computer/cpu/2 cards and this psu was on the card that sapped. Its in its original setup like that with another card same model now I dont know why that could be an issue?