Restore I-Tunes Library

The latest rounds of I-Tunes updates has seriously screwed up my library! I have about 300 songs(and counting) that I can't play or record on disc to play in my car where as before, I was able to make discs or play them. Beside these songs or albums are asterisks that note the songs are unavailable and cannot be played or they have been moved elsewhere. This is truly maddening. I need to know how to restore my library and eventually move them somewhere else. Another question: is there another reliable app where I can move my library to after I recover/restore my library? Thanx to everyone who responds.