Unistall all the graphics drivers. As said above. Type Regedit in Run and remove anything in you registry that says nvidia. Now your drivers are not present and your registry is clean. Addiitonally, I would check to see if the Nvidia folder remains in the programs folder on drive C: If so, delete the entire folder, reboot. Reinstall the freshly downloaded Nvidia drivers. It appears that that card does not have aux power. If the card were bad you would get a continuious high pitch screech from the mobo at initial boot. Try all that.
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EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.