my rock band 2 disk wont read on either of my ps2's, but the track pack will. any suggestions?

my ps2 wont read my rb2 game, but it will read the track pack vol. 2. it also wont read ghmetallica, but it used to. my slim ps2 wont read them either.

Is it scratched? If yes, there are lots of i'bles on that subject. Search for "scratch repair." Is it your system? Are there any other games, especially with pristine discs that give you trouble? We need to know more.