Motherboard doesn't matter, not sure why he asked about that.
Look at the horizontal "flat blade" part of the DVI cable. I'm guessing there are four pins around it, two on top and bottom. Those are the part that carries the analog signal in a DVI-I (or DVI-A) cable. If you have a DVI-D port which has been suggested then there isn't a part on the GPU for those four pins to go in. They are hitting solid plastic and prevent the cable from being used. You can pull those four pins out with pliers, get a DVI-I to DVI-D adapter, or just go ahead and buy a new DVI-D cord.