Graphics card problem

Hey Guys,

I have been running my system for a while now with one graphics card (HIS Radeon 6790 Turbo) and it has been going alright, but for my birthday I received another one. I set everything up and plugged in the crossfire and got going. I immediately had problems. Not only was everything graphics related much slower and glitchy, it has been messing with my computer in general. Making it so I can't see anything on my screen until it's at the login screen.

Sometimes the card works really well for a while then an hour later it acts up again.

I already set up an RMA on Newegg to return it, but before I send it I would like some opinions.

My setup:
Antec 1200 Gaming Case
Intel Core i7 920 (OC to 3.8ghz)
Asus X58
HITACHI 750GB 7200RPM
Kingwin 1000watt PSU
Antec Kuhler 920
Corsair Vengance 8GB DDR3 ram 1523MHz

Thanks
Brian

Check your PCI E slots....both need to be the same...ie 16x16 or 8x8....or PCI E 2.0 vs PCI E 1.1. Both slots need to be the same version and BUS speed.