go to Preferences > General and make sure that there is a check mark next to both Music and Movies.
Close preferences and you should be fine
I have a MacBook Pro (OS 10.6. and use i-Tunes (v. 11.1.3) I recently noticed that in my sidebar there is no indication of there being either"Music" or "Movies". My list begins at "TV Shows" and is otherwise complete, including STORE, GENIUS, and all my PLAYLISTS. I have over 15,000 songs, and unless they are included in a playlist, I can't access them. HELP!