Help!! Pioneer head unit Won't take cd's

I have a deh-p4000 head unit. Last time it worked I ejected a cd to put another one in. When i tried to put the new cd in it didn't reconize the cd player at all. There is a function button on the unit that selects tuner , mcd, and cd. The tuner comes up, Mcd (changer) comes up, but the cd player for the head unit doesn't. It used to come up even when a cd was not in the unit. ACK ! I can force the cd in and hit eject and it ejects fine. The funniest thing is the function button not bringing up the cd player. Its like it just decided it wasn't there.