I had a similar problem with my old 6870 and it turns out it was a problem with my HDMI cord/possibly port. Try using a different cable and getting rid of any possible dust that is in the port.
Thanks man. I had the wrong email address linked to this account... so it took me until recently to find out anyone had actually replied. I purchased an HDMI to mini display port adapter, as the HDMI port on the card was the issue. Everything is working great now. Thanks!