If your vehicle is showing engine suddenly stalled while driving and will not crank or turn over, here are the most likely causes and the parts you'll need to fix each one.
The alternator stopped generating electricity while driving, forcing the vehicle to run entirely on battery power until it was depleted. The engine stalled from lack of electrical power to the spark plugs/injectors, and the battery is now too dead to crank the starter.
A battery terminal or main ground cable vibrated loose while driving. This instantly cuts all electrical power to the vehicle, causing an immediate stall and leaving no power available to engage the starter motor.
The electrical contacts inside the ignition switch failed abruptly while driving, cutting power to the engine control module and ignition system. Because the switch is broken, it also cannot send the signal to crank the starter.
The timing belt snapped while driving, causing the engine to instantly stall. In an interference engine, this causes the pistons to crash into the open valves, physically jamming the engine so it cannot rotate or crank.
A massive loss of engine oil (often from a loose drain plug or filter after a recent oil change) caused the internal engine components to overheat and weld together. The engine is physically locked up and destroyed.