I have had the same problem a couple times.
The way I do it is trying to switch on and off the SONY unit, which I have.
Once I have had to turn it on and off like 7 times, also trying to switch between SOURCEs (radio etc.), try eject and load buttons.

I cannot believe how crappy these Sony units are. I love my MK3 (I guess if 2007 Jan) Mondeo, but this is the only item I hate. Does not read burnt CD-s properly etc....

Cheers,

R.