a key that opens the door turns on panel but shows security light and won't start the car?
The security system in your vehicle is doing its job and telling you that that key is not supposed to work with your vehicle. If that key was working with your car before, the resister in the key has died. If not and it has a + (Chevy does yours may not) sign on it, you need to have it paired to the car. It is also possible that your car will only accept two keys and that is a third key. Run it by your local auto parts store and see if it was designed to work with an ignition system or if is just a door key for back up entry. Good Luck
thanks, will try your ideas lois