mp3 on windows media

hi my wife likes to play mp3 on the windows media player,but she’s done something to stop it registering on the media player,the disk has over 100 songs on it its not the disk as it works on other xp machines and i cant find anything wrong internally wrong with the running programs. somebody help me have a quiet life,the only way i can get it to play is run is to open the cd itsself and run them one at a time and other music programs recognise the cd and play the music. HELP!