Your monitor, since it has both ports, is probably "hard wired" to receive signals either DVI to DVI or HDMI to HDMI. Certain monitors can act funny with adapters. I know my ACER 22" doesn't like to stay sharp (noticeable fuzzy) if I use its VGA port to DVI using an adapter. However, if I go straight DVI to DVI the picture is extremely sharp.
What is the brand of of your videocards? If they're XFX, XFX is very good about helping you to troubleshoot and they have always resolved issues for me.