I was driving my car and suddenly stopped. on 2004 Chevrolet Trailblazer

I tried to turn it on and would not start. The gear shift turned loose and car would go on reverse when I pressed on the brake.

Asked by for the 2004 Chevrolet Trailblazer
Does it crank over when you try to start it? Do all the lights come on with key on? Need more info.