You have had a loss of power to the radio (such as when the car battery is changed), or the radio has been replaced or disconnected from the car's wiring harness. This is a theft deterrent because the stolen radio is useless to someone without the activation code. This code can be obtained from a dealer or it is found on a small plastic card that is part of the original owner's materials. Number is usually 5 digits. When you turn on the radio and the readout says 'CODE ', enter the number by using the numbered station selection buttons (which are numbered 1-2-3-4-5-6). If the radio beeps when you are entering the number, start over. If it keeps beeping, you have the wrong code number (which might be the case if the radio has been replaced). Note: The 'CODE' button located on the small computer face to the right of the radio (with the date, mileage, temperature, etc) has NOTHING to do with the process or the radio 'CODE'.