cd rejects to insert

Take a look at this article it is similar

http://support.apple.com/kb/HT2801

Reset the SMC

see

http://support.apple.com/kb/ht3964

Make sure their is not a disc already in it

see

https://discussions.apple.com/thread/4180892?answerId=19175550022#19175550022

Specific troubleshooting Below are several possible symptoms you may see. Follow the steps for the appropriate symptom to figure out whether the issue stems from the drive or the media. Be sure to inspect discs before use to ensure they are not cracked, scratched, or otherwise damaged. Inspection should include the inner ring of the disc which should be smooth and burr free. A disc with physical defects may become stuck in or cause damage to the drive.

Doesn't accept discs

1. Be sure to check your disc to make sure it is flat. You can check this by putting the disc upside-down on a flat surface. If the disc is bowed up on any side or in the center, do not use the disc because it might get stuck in the drive. Do not use discs that have anything attached to them or dangling from them (such as "sweeper" or cleaning discs).
2. If the drive struggles when you put in a disc or stops part-way, carefully look at the disc for labels that may be interfering. If there aren't any raised labels then try putting the disc in a few more times.
3. Try another disc to see if the issue is being caused by a specific disc.
4. Make sure you insert the disc far enough for the drive mechanism to activate. You need to insert discs nearly all the way before the drive will activate and pull them in. If you don't completely insert a disc, the drive will reverse and push the disc back out.
5. Allow the drive one or two seconds to accept the disc while it is fully inserted.
6. Reset the System Management Controller (SMC).
7. If the drive repeatedly does not accept discs, contact Apple or an Apple Authorized Service Provider, or make an appointment with an Apple Retail Store.