Check in LimeWires options what directory you have set for the Library.
the Library is usually the folder you have songs in that you plan to share over the internet. These settings have changed a couple of times over the last few versions of LimWire so it shouldn't be too hard to track down these errant files.
another way to find them is to go into the search section of your start menu and in the find section type the name and extension of a song you know you should have. Something like: xxxxxxx - xxxxxx.mp3
You will usually get a result telling you where you have your files stored.