99 Stratus won't turn off

I have a 99 Stratus and when I start the car and it will turn over, but not acutally start up for about 5 seconds. When I turn the car off and take the key out of the ignition, sometimes it will shut off within 5 minutes. Other times I have to go under the hood and pull a fuse, but when it shuts off, it shakes like it's in the middle of an earthquake. I've had it in several repair shops, including the dealership, and nothing has worked. Any suggestions, because I'm lost??? :eek7: