Need New Card

Ok so heres the deal,

I have an ASUS EAH4870 DARK KNIGHT Edition card that is giving me a world of troubles. First I could play games for about an hour until the heat overload light came on. Screen would go black and i was forced to restart. Well this problem then started kicking in only minutes into playing. I took it to my local computer shop and they said they put it on a test bench for 22 hours of furmark and it never had a problem. Now i know this could be my cooling but i have a front case fan a side case fan and two rear exhaust fans all running at max speed AND the cards onboard fan running at 100% speed. Now when i went to throw this card back into my system today i got nothing. the computer will start i can hear the hard drives running but absolutely no VGA output. And the ONLY thing to have changed is the card being removed and reseated. all power cables are connected and ive tested the power supply at 12.4 Volts on all rails. WHAT IS MY PROBLEM!!!???

System SPECS:

Intel Core i7 920 @ 2.67Ghz
MSI X58 Pro MOBO
OCZ 700 Watt Modular Power Supply
ASUS EAH4870 DARK KNIGHT Video Card (1 GB)
6GB OCZ gold DDR3

AND IF ITS NOT REPAIRABLE PLEASE SUGGEST A NEW CARD (I was thinking of the 6850 or 6870)