2000 Mitsubishi Galant Repair Code?

Took car to Midas because of undercarriage noise. They fixed the noise problem (by welding shut a hole in a pipe) but then I couldn't start the car although I've had the car for about four years and never had any sort of starting or battery (or radio) problem. Midas told me the problem was a corroded terminal on battery. Took the car to Sears but the radio wouldn't work. Sears replaced the negative cable and the battery but the radio still wouldn't work. Service man told us the radio was asking for a code and I was told to give the VIN number to Mitsubishi and they would give me the code. Is this possible? If it is, who do I get the code from and what do I do to get the radio working?