Make sure wmp is your default program for audio; apply the same principles here but apply to wmp & mp3:
Setting Default video app
Go to Tools>Options>Player & untick option & press apply button. This won't take effect until next time you open LW.
Make sure you have the latest codecs for wmp. For m4a files you'll need the 3ivx codec go to
http://www.3ivx.com/ & go to dwnld page & look on top right of page.