Are you previewing the files during download & if so, do they play then? Which player are you using?
Are you using your AV program to scan files that you've downloaded, before you open them? You should

If you're using LW's player, disable that (tools > options > player) & see whether the songs play when you use another player.

Make sure that you're not downloading infected files.
http://www.gnutellaforums.com/download-upload-problems/84503-new-virus-limewire.html
* WARNING: Viruses on network you should be aware of! *

Check the files with Bitzi. People don't rate music files too often, but if the files are bad people may have rated them to warn other users.
How to use Bitzi