You shouldn't have deleted those files. The files listed in your media player are a playlist, i.e they link to the original file. If you delete the original file there's nothing for them to link to. So the files won't play.
You'll need a file recovery program to get them back:
DELETING FILES FROM LIMEWIRE LIBRARY-DON"T! - File recovery advice!
Just FYI: In the Beta Version, files deleted from the library go to the recycle bin.