The most common cause is a faulty laser. You may be lucky and find that it responds to a good clean. Try a DVD laser cleaning disk.
If you or your passengers smoke this could well be the cause. A film of nicotine covering the laser lens is quite common.
Other than that it is a pro job.
Colin
February 2007
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix in-car audio.