Have you tried going to you folder that you have your songs stored in and double-clicking them or right clicking and telling them to play with whatevermp3 player you have assigned to that file extension?
Sometimes mp3 files are not set to open in iTunes and you can check this by going into the start menu and going through "Default Programs" to check what file extensions are assigned to which application.
Apart from that all I can suggest is for you to un-install and re-install LimeWire and see what happens them.