Try disconnecting the battery for 5-10 minutes and then connect it again. It may reset the computer and allow it to start. Borrow a code reader from a local auto parts store that loans out tools. Autozone does this but not all have code readers to borrow. It could also be the chip in your key went bad which would do the same thing or there is something wrong with a sensor in the system. A code reader would help zero in on that sensor and many hardware and auto parts stores can check your key for you. Good luck.
Answers & Comments
Try disconnecting the battery for 5-10 minutes and then connect it again. It may reset the computer and allow it to start. Borrow a code reader from a local auto parts store that loans out tools. Autozone does this but not all have code readers to borrow. It could also be the chip in your key went bad which would do the same thing or there is something wrong with a sensor in the system. A code reader would help zero in on that sensor and many hardware and auto parts stores can check your key for you. Good luck.
Contact local GM dealer to deactivate or repair the problem. That will be the quickest way to get you going.