The first thing that comes to my mind would be to use a regular DVI or D-Sub to connect the monitor and computer and then manually set up the HDMI connection with your graphics card and monitor...try that and see if that'll work. I know that when I hooked my plasma into my vid card, I had to go into CCC and set it to send the HDMI signal to my plasma...
Also, just to clarify, this isn't a new build is it? If so, you might be using on-board video...you'd need to set it to PCI-E in BIOS...