IF your running those cards in SLI, like i think you are. Power down your PC. Open your case. Ground your self. and reseat the SLI bridge wire. If you dont know what it is, its the wire connecting the two cards. Something like this : http://www.hothardware.com/articleimages/Item1120/790i_SLI_9800_GX2.jpg
( Meaning take it off and put it back on. Make it snug, not loose.) Then close up and try to see if any change. I had similar problems with my 8600gt SLI rig.