Well, I hate being a giver of bad news, but it sounds like the cd drive has stopped working on you do to some kind of hardware failure inside the drive itself.
To be sure, try different types of cd's, cd-r's, dvd's, whatever your drive is supposed to be able to read.
If you have OS X, try cd's there and then in OS 9 as well. See if the problem persists.
Also be sure that its not the software running on your system causing it to be spit out (i.e. extension not loaded/corrupted, etc.) you may have to reinstall to confirm its not software.
After confirming all of this its safe to say its a goner if it still is going you trouble.
Taking it to an AASP to have it replaced will cost approx. $200 or more depending on the provider and the actual model/part # unless of course its under warranty
Hope that helps
- Taz