I have a Focus and have the same problem, but I know why. My 3yr old put a couple of coins in the slot and they are stuck in there. I've booked my car in to a Ford dealer to see if they can fix it. They most probably will, but I'm sure it's going to cost an arm & a leg. Alternative would be to get new audio fitted. Crazy really when you think about it! All you need is a special tool to remove the audio and then shake the coins out. In my case, anyway. Good luck with yours!
Elise
August 2009