okay, managed to sort this problem out.
i tried to eject the cd's. i used a thin plastic ruler and inserted it into the cd slot and jingled it around. tried pushing down to activate the eject mechanism, but no joy. then pushed upwards on th left, and this must have activated a switch, as there was a click. the cd then started to play. i pressed and held the eject button, to activate "eject all", and all the cd's were ejected.
The cd's ejected were all cdr -burned cds. lesson learned, i will not be putting in cdr's, and will stick with bought cd's.
Now working fine, and saved the hassle of replacing /fixing the head unit.
