Take a look at the front fascia of the CD ROM drive.  You should be able to see a small hole in it. 


Take a paper clip, unbend it  and push the end into the hole.  It should release the manual catch on the drive, allowing you to retrieve whatever is jamming the drive.  If the drive has failed it is relatively cheap to install a new one and there is no need to lose the disc that is inside it.

The unbent paper clip is one of the most useful tools in the PC repair man’s toolbox.