Vauxhall rad/cass code entered incorrect too many times?

Im selling my father in laws 1997 vectra estate with a radio code that I suspect has beeen entered incorrectly too many times & now the set will not funtion at all. Ive checked the fuse in the back of the set (its a Pillips CAR400) & thats fine & when I turn the lights on the light behind the volume knob lights up so there is power to the set OK. Can anyone help - in the manual it says you have 10 attempts then it stops functioning - but Im reluctant to take it to Vauxhall as its not my vehicle.