I had the same issue with two cards, tried two monitors and two slots on the mother board. I tried a HDMI and DVDI cable on both monitors. I have all the latest drivers and all the windows updates, its happened with two installs. It required some force to get the cards in though.
I played around with the color settings etc in Catalyst and the monitor and its not as bad, I have not tried a game yet though as i've spent all my free time re installing windows and testing :-)
Thanks for you help