To make sure the problem is actually your video card, try getting another card to change out. If that backup card works, then you know that the card you are working with now is defective.
I commonly switch parts out of systems to see what is working right and what is not. This is one method of troubleshooting. If the problem with your video card still persists, it could be the following;
Your clocks could be set too high: or, you could have a bad overclock. If you by any chance overclocked, drop your clocks back down to stock.
You may be running at PCI-E 8X instead of 16X.
Also, you can chekc out these sites for consideration;