Radio/cd player not accepting cd?

Hi. Recently bought 2nd hand Ford 6000 radio/cd player which refuses to accept the disc. Can push the disc in manually but nothing happens. Eject working ok. Seller, who I believe to be genuine, says cd player was working ok when taken out of his vehicle, and can only think that unit has received a knock in transit resulting in the belt drive being disturbed. Unit looks in perfect condition and radio works perfectly. Any advise would be much appreciated.