Are you sure you've got your system volume turned up.
just joking! lol Well, LW's media player is not the most reliable, but still ... it works for most people. Why not open it with your default audio player instead?! Go to LW's menu Tools-Options & Player. Untick option box. This 'should' allow your default mp3 player to play your music. If probs, select an mp3 file & go to File-Properties & change default app to open it. For more mp3 players see:
QCD (Free) or else
iTunes for Windows (Free) or other. There's plenty around incl winamp, etc.