Got an odd issue here - the Superdrive on my Macbook is reading and writing DVDs just fine but if you pop in a CDR, it just tries to read it three times and then spits it out. What's up? The Superdrive messed up?
Sounds like the CD lens is either not working or is covered in dust. If it is under warranty I'd take it in. If not, you can try just blowing some compressed air in, which may clean off the lens and allow it to work.