Nissan Micra 2003?

Depending on the make of radio , what you may have to do is to switch it on as though you are going to enter the code ( pressing ON switch +another button perhaps? see below ) then leave it for at least one hour . IMPORTANT ..Do not disturb it as it will start the one hour again )

Entry info here

http://www.davidsonelectronics.co.uk/code_entry.htm

RegWorts
June 2008

You may have to leave ignition on for that 1 hour.

David
June 2008