I have a 2001 Pontiac with the same problem. Security light always on and then it wouldnt start. I had a sensor replaced, and the Mechanic said evenually the ignition would have to be replaced. 300.00 later, and now the light goes on again, and once in a while it wont start. Here is a trick, so you dont have to wait 2hours. Put the Key in, and turn it over half way, like your listening to the radio, but dont start it or even have the radio or anything else going. The security light should be flashing at this point, wait 10 minutes, turn the key back off, take out of ignition, then start the car. Should be good to go. Good Luck