am havin a bit of trouble with my itunes, i know i havent deleted any of my music but when i try to play some from itunes i get a little exclamation mark and a message that says the file cannot be found. this has happened on loads of tracks, and they seem to have vanished from existance!! cant find onmy pc anywhere either! whats happening? i know i have had them on my ipod but when i sync they go!