Just check and see that WMP is still your default player...
Go to your shared folder (outside of Limewire) you will find this folder by clicking on one of your files in your LW library and clicking explore...
Right click on one of your MP3 files
Select open with
Select choose program
select WMP
and tick the box that says always use this program to open this file type
Select OK
You may also need some updated codecs...
For XP this codec pac is very good
Download XP Codec Pack 2.0.8 - XP Codec Pack is one of the most complete codec pack
Or for Vista this pac
Vista Codec Package v4.4.7 Beta 4a (freeware)