[twdz28]

Do you want the security function to work? As a test, to see if it's the key switch, measure the resistance of the key pellet. Get a resistor close to the value of the pellet. Find the orange jacketed wires at the base of the steering column. Put the resistor across the contacts of the wires. If the light goes out and stays out, you have a problem with the key switch. If it still has the same problem, then the problem is with the wiring to the PCM or the PCM itself.
camaro's and corvettes are bad about the wires breaking at the key cylinder. since it works on and off thats probably whats happening...it's a pain to fix them, so what i would do is either A. take the pallet and measure the resistance go to radio shack and sauter the resistor in at the bottom under the dash... they are two white wires and have a connector at the base of the steering column. or B. you could just sauter the actual pallet in there....i don't recomend taking the column apart because its a tough job... there are circle clips on the steering shaft that are a pain. that will save you a lot of money, but your security system won't work... do you unlock your car with your key ? or with the keyless entry? next time get out and unlock the car with your key and see if that fixes it.. if so you'll need a new key fob!

You are dealing with the VATS. (vehicle anti theft system)

The VATS module verifies the value of the pellet on your key. If the value is not correct, the car will not crank.

If the key pellet is dirty, or the contacts inside the lock cylinder are worn it will fail and show the problem you saw.

Try to clean the key, then try a different key. If that does not work you may need to replace the lock cylinder.