First , make sure you have the correct code for your radio ( Check it by posting the SERIAL NUMBER here for confirmation...Hopefully it begins with M******). Then try a "reboot" by disconnecting the fuse (or battery ) for 5 minutes, reconnect , then enter the code. If it doesn`t work (with the correct code ) then try leaving the radio switched ON ( UNDISTURBED) for several hours(overnight if possible) and that might reset it automatically Failing that, it means that either the radio has been recoded in the past or the radio is completely locked up (due to too many wrong attempts) so will have to be taken into a Decode Specialist for unlocking +recoding...(Perhaps cheaper at this stage to buy a used replacement off ebay?) ..Please post back here whether successful or not ...and which suggestion worked !..
RegWorts, May 2008