No sound on Windows Media Player

For some reason, I do not get any sound any more with videos using Windows Media Player. It used to work fine. I can still get audio using a player such as the music player from www.launch.com , so I know the computer is capable. I have re-downloaded the Media Player, but still no sound. Does anyone have an idea how I can get my audio back? Maybe I downloaded another program that is conflicting with it or something. I can't figure it out. Thanks.