There are really only 2 possibilities here. One is if the CD you are trying to use is a burnt copy and/or has a label attached to it, it can cause this. If that's the case, try a new original CD. If it still doesn't work, the unit will need to be either sent in for repair, or replaced. If you have further questions feel free to reply.
WHERE IS THE AUXILIARY INPUT ON THIS UNIT?
The 12 pin plug in the back of the radio is for the aux input. You will need this interface.