How do you turn off the anti theft device on a 2000 Alero?

You have to know your secret code and use it to turn it off. I am having the same problem. I just bought mine from a friend whose grandma had it and they replaced the battery which caused the vehicle to freak out and get locked up. Why me? I have no radio and I am a singer!!!! What do ya do? I'm a Canadian. Well I guess I will just have to take it in to a GM dealer.