1999 Chevrolet Cavalier 99 Z24 Running Perfectly Other Night Driving Home

I have a 99 z24 cavalier and it was running perfectly. the other night i was driving home, heard a scraping noise once, turned left around a corner, and the cars computer fell out and i ended up driving over it and the car completly stopped and shut off. Towed it to a mechanic and the mechanic figured i would need a new computer, so i got a new one and it didnt do anything. the car will roll over but not fire up. the car also wont respond to the code reader when it is hooked up to it. what in the world would the problem be??