Turn the unit off.
Press the eject button with one hand and then turn it on holding the eject button in.
If you are very lucky it will come out 1st time, more likely though it will take many attempts, so just keep turning it on and press eject at the same time.
It took me over a week to get a CD out on one occassion !
This seems to be a common fault, I am giving up with mine and buying a new CD/radio and it will not be a VDO CDR 500 !
JW, March 2009