Leave radio switched ON ..UNDISTURBED for at least INE HOUR and it should reset itself allowing you to enter the code.
Make sure you are using the correct code.
If not sure ask a NEW question quoting radio MAKE , MODEL and ALL the SERIAL NUMBERS on the radio casing.
Instructions on how to remove from dashboard found on this website
www.tinyurl.com/4ydhop
RegWorts
August 2008