HDMI does not require drivers its the same signal as DVI. Did you plug in the GPU power connector, and have you tried both DVI Ports? DVI and VGA are not compatible and the adapter will only work on the DVI-I port that has the extra analog pins to drive VGA. You are plugged into the GPU not the board right?
Edit: re-reading that, PLEASE tell me you weren't plugging and unplugging power with the system on