First make sure that you do have the correct code (Ask on this Help Board to check) One method that might work is to switch the radio on and leave it on , undisturbed , until it resets automatically. If it switches itself off automatically before it has reset itself , then the radio will have to be taken out of the dashboard and connected up to a battery (undisturbed )on a workbench and left overnight.(more than 11 hours ) Please post back here whether this advice was successful or not.
RegWorts, May 2008