There's currently a bug in winamp where if your computer was turned off without shutting down while your winamp client is open, the music library becomes corrupted and lost all songs.
Here's what a broken winamp music library looks like (click the images to enlarge).
To fix the broken music library,
1. Go to Options ~ Preferences
2. A small window will popup, locate Local Media under the Media Library and click Clear Media Library
3. Click Yes.
4. Now your broken music library is cleared, it will now be emptied.
5. Now, relocate your music folder to fill up your music library. Click File ~ Add Media to Library...
6. Find the folder where your music files are stored and click Add.
7. Wait until the loading finishes.
8. Your winamp music library is now back to how it was before.
