If your car CD player is not recognizing the CD you insert into your car CD player, then try some of the solutions i recommend to fix this problem:
1)Is the disc you are wanting to play on your car CD player a original? Some CD players don't allow back up burned copies to be recognized as a audio format disc. Try to insert a original CD into the car CD player and see that works. If it does work, it shows that you can't play burned audio Cd's, probably because it doesn't support CD-R formats. Sometimes, it can also be the brand of your disc's your using to create you own audio Cd's. Cheap brand offer no reliability and many people still want to buy then because there £4.00 cheaper. So i suggest you make another burned audio CD, this time burning at a lower speed and using better quality disc's.
2)Try cleaning the disc.
3)Examine the disc itself, does it have bubbles inside it or scratches? If it has bubbles, the disc is permanently damaged., which is the cause to the problem. If it has light scratches, you may be able to remove them using toothpaste.
4)Clean the laser, using a cleaner disc kit.