I have seen this before myself, it was a strange configuration issue with the game, I rebooted my pc, cleared my temp files (from the c:\windows\temp directory), and reentered the game fine.
Assuming that didn't work -
1. use a cleaning cd on your cd drive (every 6 months or so)
2. you said the cd was fine, but how did you examine it? you have to tilt a cd in the light and check the reflection, otherwise some scratches and dust are almost impossible to see. Even if you don't see anything, use a lint and oil free cloth to swipe the cd, blow on it to remove any small dust particles, and retry it.
3. if that doesn't work, try a cd repair kit, use the solution on the cd very sparingly if you cannot actually see any scratches (nearly invisible ones can still be fixed this way). I've corrected a number of problems with other games this way.
