CD's will not play on my Sony 6CD player (54 Reg. Mondeo)?

The problem first started on a long journey when I had been playing CD's for around 3 hours. The CD stopped playing and the unit auromatically switched to radio. The next time the fault occured The CD player had only been playing for a couple of hours. The duration of played reduced over a period of time until now it will not play CD's at all.