I had the exact thing happen to me. The security light flashed on. Try putting in the key, turning until everything lights up, but dont try to start it. All the lights will flash on and then go away. Do this until your security light also goes away. If it goes away, this is your one chance to start the car. Dont turn the key back & then try to start! Turn the key forward & start from the position described above.

You can only retry once every 10 min or so, or the security will lock you out of the computer. So just keep retrying every 10 min or so. I finally got mine started after 1 hr of doing this & made it straight to the dealer where they replaced the ign cylinder. There is a ground wire strap that breaks often, causing this. Thants what the tech told me. Good luck.