My cd player doesnt work when the car is running?

My cd player and radio works just fine when the key is just on and the car isn't running but as soon as you start the car the cd player doesn't work. i figure its got to be something in the head unit or a short in it somewhere, I'm no wiring expert or stereo genius so I really don't know. Any info or input would be greatly appreciated, thanks for the help guys...

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Does the unit not turn on when the car is running? The only thing that I can think of is a bad voltage regulator. Some radios will not work properly if they see too much voltage. I would take the car to a autoparts store and have them check the voltage when off and when running.
If it's a after market radio. You need to make sure you are getting a constant 12 volts to the Yellow wire. The red wire should only get 12 volts once you turn the key to ACC position. And of course make sure the black wire has a proper ground. Those are the three most important wires to make the radio work right. If that's all right then it's something wrong with the radio
Great information, cant wait to take a look at the wires and see what kind of voltage its getting. Its weird though when the car is running the cd player is actually working, it turns on but theres no sound, it runs through the songs but with no music if checking those things doesn't work then I'm probably gonna assume its the head unit.

This is unusual. There are no factory radio wires that change when the car is acc mode vs running. As long as the red wire on the back of the deck is hooked to accessory 12volts, the yellow wire to constant 12volts, and the black to ground, you shouldn't have any problems. Do you know if you have a factory amplifier? That would be the only other thing that could be the cause of this type of problem.
I didn't get a chance to mess with it today but it does have the factory amp and my friend who put the cd player in did all kinds of wiring to either make the cd player work with the factory amp or bypass it, I'm not too sure. I would think it would be weird for the amp to not work when the car is running but it works when the key is on... Thanks again for help, hopefully i can look at it tomorrow

sounds like it's your amp turn on wire or antenna wire. Usually blue and white from the head unit and Blue. Try connecting the Blue an the Blue with white together from the head unit. When you play a cd the radio will not send 12 volts to the blue wire, only when you play the radio.
Another way to check and see what may be wrong is to connect the wire that is currently hooked to the blue/white and temporarily connect it with the yellow to give the amp constant 12volts. That would rule out a problem with the amp turn on lead.