As you may already know, it is locked because of too many wrong codes being entered so the first thing is to make sure that you have the correct code.....Then one method that might work to unlock it is to leave the radio switched on (UNDISTURBED) for up to 12 hours then it might unlock itself automatically.( You have to be patient !) If this doesn`t work , then I`m afraid it will have to be taken into a Decode Specialist to electronically unlock it...but it might be cheaper and quicker to buy a replacement (with code ) off Ebay......Please post the outcome back here so that we can confirm whether this method does work.
Note : The entry procedure can be found here
http://www.davidsonelectronics.co.uk/code_entry.htm
RegWorts, May 2008