Probably a defective ignition switch, based on your dandy description. It's a common failure item, but not for this symptom. I was surprised by a recent post where the person said the switch took care of his problem, and it was under 50 bucks.
Replacing the switch isn't hard if you can follow the directions in the service manual. You'll need to release the lock cylinder and put it into the new switch. It's much harder to describe than to do. The switch is held in with three tamper-proof torx screws, so you'll need a special screwdriver bit. The Snapon, Matco, Mac, and Cornwell tool truck guys can supply those.
With the right tools at hand, the job takes about 20 minutes.
The lock cylinder should be inspected too. There is a round cam on the end, about 5/8" in diameter. When the cam cracks, it doesn't turn the ignition switch far enough. The very common symptom is the dash lights come on like normal but the starter won't crank the engine. It might crank if you turn the switch real hard, but you risk breaking the key. If this is the cause, the engine should turn off if you run the switch all the way back to the Accessory position. There is a repair kit available to replace just the broken cam.
When it doesn't turn off as expected, observe if the radio display is still on. If it is off, the ignition switch moved far enough that the engine should be off too, so suspect a defective switch.
Wednesday, March 25th, 2009 AT 3:20 PM