I have itunes installed on a 64-bit windows 7 laptop. Used to work. Now it doesn't. When you click play on a song, it the icon changes from a triangle to the two rectangles (play to pause), but it doesn't play. Many songs. They show as mpeg-4 protected files. Have repaired itunes, upgraded to 11. Removed it. Re-installed it. Other applications can play. Itunes will play movies, but not songs. Any suggestions?