My first thought would be a virus... do you run AV scans regularly?
Have you checked to see whether your saved folder is still around (by default it's C:/Documents and Settings/your name/Shared) or used the computer's search to look for some of your music files?

You could try reinstalling Java (use the offline installer)
http://www.java.com/en/download/manual.jsp

then reinstall LW using it's offline installer
http://www.limewire.com/english/content/download.shtml

If things are still screwed I'd suggest going to Norbiesworld & getting him to check out your computer. If you go to his site & register, follow the directions for free computer help & post a Hijackthis log, he'll be able to tell you if you have a virus problem. It's all free.
Norbiesworld (click on link)