Dvd player and 6 disc cd changer for cars

Question

hi i have a problem with getting my dvd player to play on screen the screen works because i can see what radio station i an on. i installed it and i can play music and hear the sounds of my dvds playing but cannot see the films and cannot change from one cd to the next i know i haven't given you much to work with but any suggestions will be much appreciated thank you

barry ferguson.