Are you shutting down all non-essential programs (especially anti-virus) before starting the game?
Do you have more than one optical drive you can try? If the copy protection finds the install disk first it will not keep looking for the play disc, but that should not be an issue for any CDs not labeled 'Bey_Dev'. Maybe remove any other CDs anyway, if present.
Did you check if the drive is having problems with other CDs? Did you check for dust, etc that might have gotten into the drive and be interfering with reading the CD?
Either something has changed in the system that is causing a conflict, or there is a problem with the CD or the optical drive.