1. you have not yet accepted the eula for windows media player
2.you dont have the codec needed to play the .filetype you are trying to use
3.you are attepting to play burned disc and is a non support disc type
1.click start and type windows media player in the left hand colum it will populate double click windows media player. check the check box for i accept
2.download codec for movies and stuff http://www.videolan.org/vlc/
3.buy an external drive