Hmmn. In terms of playing your songs, I recommend downloading and installing WinAmp from:

www.winamp.com

Once you have this installed, you should be able to launch your files from your library successfully.

In terms of the other (more serious) problem, try completely uninstalling your current version and downloading and installing the LimeWire 1.6d beta version from:

http://www.limewire.com/index.jsp/download_beta

Let us know if you have any more problems with the latest version.