1999 Grand Am Gt not starting?

The PCM is under the dash on the drivers side near the steering column. I doubt that is your problem though. You need to check the DTC's (diagnostic trouble codes), that will send you in the right direction. If the vehicle isn't cranking over at all, it wouldn't be a plock issue, as it cuts the fuel pump off, so it would still crank over, just not start. The most likely cause of your problem is a faulty BCM (body control module) it is under the dash on the penger side. It will have to be programmed after replacing, but the symptoms you are experiencing, i.e. the door locks, and radio in-operable points towards a BCM. The BCM controls these things. Also, if you do in fact find that it is the BCM and have it replaced, check to make sure there hasn't been any water intrusion. GA's are notorious for water leaking on the BCM and corroding the connectors and killing the BCM. So, if you do find corrosion, fix the water leak too.