LW's Media player is Horrible at Best.
You could try a different Media Player. VLC Media Player has Codecs Built in and is Highly recommended here on the Forums. VLC is primarily a Video Player, but will Play Most Audio Files as well.
See the Link Below that LOTR's has put together for other options and suggested Media Players.
CODECs list for Movies/Alternate players / Video help forums/ video-mp3 fixers
Hope this Helps.
