Hello. I just purchased a 2000 Cadillac STS. I have always liked that model and was so excited. I forgot to research how expensive it is to own a cadillac. I am receiving a message that says "Service Theft System". The "security" light is on. When I try to start the car it will not start. The automatic windows, locks, etc. work. The battery is fine. Can anyone help. I don't want to pay mega bucks to take it back to my local dealer. Thanks so much!