Note: before doing system restore I recommend you backup your important data on your C: disk (commonly stored in "AppData" folder). Just to be sure.
- better and more preferred route would be to avoid Windows Media Player altogether. There are much better programs out there and I would personally recommend Media Player Classic. The downside of this one is it requires codecs installed on a system. You can get whole package if you download "K-Lite codec pack" (google it). The other solution which comes with a number of built-in codecs and good to use is "VLC Media Player" (also called "VideoLAN player") all in one solution. For playing audio files, WinAmp is great.