2000 Geo Prizm engine cranks but doesn't start

while on the expressway, the car turned off all of a sudden. the lights and radio were still on but the car was off. once i stopped i tried turning the car on and noticed that the car was cranking but it just never turned on. i used some starter spray and the car turned on but the engine had some knocking noise and it shook really bad. what could it be? thanks