I believe it's the cable. The first cable u described is a single link cable. The cable your monitor and graphics card are showing requires a dual link cable.
"All modes that require more than 24 bits per pixel, and/or 165 MHz pixel clock frequency must use dual-link mode"
Try the dual-link cable and i bet the issue is resolved
. Should be as simple as taking it to best buy and having them plug it in. Quick and easy solutions first. Then worry about replacing parts/monitor if that doesn't help.