1999 Pontiac Bonneville security light

If the security light is on, then the system has shut down the engine. What you need to do is have it checked by a dealer. THey are the only ones that have the proper equipment to identify where the problem is coming from. THe only thing you can do is try a different key. If that doesn't work, turn the key to the run position for 10+ minutes and the car should start.

Let me know what you find.

Joe