You will need to remove the radio/cd player to get the serial number as they are unique to each radio, there are various methods to remove the radio depending on the make of the radio, go to your local Halfords or car audio shop and they will advise you what tools are required normally they are less than a fiver or they might remove it for free.
When you have the serial number post a new question quoting the make/model of the radio and the serial number and someone will possibly be able to give you the keycode
nigel, August 2012