Just wondering, did you plug the power connector for your video card? I think it should either be a 4pin molex or 6 pin PCIe. Also, have you tried both DVI port on the card?
EDIT* Also there are different DVI format, do you know what DVI format the port on monitor is (DVI-D, DVI-A, DVI-I)? I know that the 7950GT should be DVI-I. You might need the right cable else they won't work.