Hmmm... an interesting problem you've got here.. the first thing I would suggest is maybe trying a different video card driver then the one you currently have installed.. it sounds like that would be the appropriate place to start.. if you don't mind my asking, which vid card do you have? and which driver are you using for it? once I know a little bit more about your gpu I can offer some more advice..
Is everything else working alright on your system? Any "out of order" things in Device Manager?...