Your car uses a VATS system . That is you have a chip in your ignition key. I have run into this on the older models where the key becomes worn from use and does not make good contact in the ignition switch. You can try locking the car with the key and unlocking it again. Then try to start the car again. This works by reseting the security system. Also you can get a new key made that fits tighter in the ignition. Be sure they have the same value chip in both keys. If this does not help you will need to see your dealer and have the security module replaced.