Have you checked the back of the head unit? You may also need to check the back side of the plugs in the wall. It is possible the Yellow wire has come loose at the back of the unit or the back side of the wall connection.
Our Greyhawk had a Magnadyne head unit, I don't remember the model. It had a built-in DVD player with a 7" screen. Our unit had a standard 3 plug RCA - Yellow, Red & White. Picture and sound quality of the Magnadyne was poor. If it isn't a lot of trouble, I would recommend a separate DVD/Blu-ray player and just use the Magnadyne for radio.
-Michael