Videos too dark

Recently every time I open a program to play a video, whether it is streaming or from my hard drive, it is way too dark. The desktop is fine, with the same amount of brightness. When I open up my nVidia control panel it fixes itself, until I close it and open a new video, then it is dark again. It happens with streaming video, dvd’s, movies from my hard drive, and tv from my dvr. Any ideas what the problem could be? My monitor and video card and whole setup is only a few months old, and this has never been a problem until a few weeks ago. If you can offer any help I would appreciate it. TIA