So, you want to take a few screen-shots of your favorite movie in Windows Media Player, press PrintScreen key, paste it in your favorite image editting program(Like Windows Paint) and you get a black screen. The reason for this is due to Hardware Accelleration. To turn off Hardware Accelleration, just follow these directions:
   1. Open Windows Media Player
   2. Tools -> Options
   3. Go to the Performance Tab
   4. Move the Hardware Accelleration Slider to None