Does it play the tuner but not the CD?
If it so, the problem is directly related to the CD deck. If not, the problem could be a sensor or any number of other components that may have overheated.
Try to reset the unit. Most of the time this error is an electrical problem not fixable by the end user. But it is worth trying to reset the microprocessor and see if that helps.
Here is a diagram of where the reset button is at. Press it in with the tip of an ink pen or paperclick, whatever you have that will fit into the little hole. Just hold it in a couple of seconds. Be advised that when yo reset the unit, you will loose all things in memory like the correct time, preset radio stations ect.
If this does not help you will need to have it checked out by a good repair center. These Alpine radios are very good radios and are worth getting fixed unless the estimate is close to what you paid for it.
good luck, I hope this helps. if so, a good rating would really be appreciated. You can always ask me for more help if you need it. I have been repairing car and home audio equipment for over 17 years.