DO a search on your computer for mp3. THis will locate all mp3's on your computer so you can determine what's what & what's where & where any missing ones mighta gone. So once you sort that out .. you can create a folder & put files you wanna share into it .. then go to LW's library window, menu File>Add Folder to Share & direct it to that folder.

By the way I hope you're the admin of your computer & no one else can log in as admin. Thus they can't access your files if you save them to your safe user account area.