Yeah I had a problem similar. I have a 6800 gt, and all i had to do was right click on desktop, then go to nvidia display, then to C U. After that, go to color correction and then i made sure 'overlay', 'desktop', and 'all' were set to advanced mode. This fixed my problem. My video's were a bit dark, but all you have to do, is in the 'overlay' option, pull the middle slider thats on the graph, up about 1/2 way to the top, from its CURRENT position, which should be in the center. Run a video in the background and mess with that single slider. Hope this helps!
Side note: make sure everything is set to defualt then mess with slider.
Newbie since 2005.