How do I get my AUX to work on my Cd player in my car after i change my battery?

Well, my car kept on dying because i needed a new battery. On my pioneer Cd player it will only let me listen to the radio and a cd. It use to let me listen to Radio, Cd, and then the AUX. I guess i need to reset it but i dont know how to. Ive looked on the internet tryin to find out how to fix this but i cant find it.