I had a similar problem with an old clamshell iBook. I put a CD in and the drive spins up, but after 4 or so tries, I get a message saying it cannot read the CD. If I put in an audio CD, the CD mounts and plays just fine. The profiler shows that I have a CDROM drive and gives all of it's specifications.
I would first try to startup off a bootable CD. If that fails, your only option is to attempt to clean the lens. After doing so, try several of your best quality (no scratches) CD's (both audio and data). If they fail to mount, your optical drive is bad and will have to be replaced.