What are the reasons for the engine not turning?

[MacCharlie]

The reasons for the engine not turning are: 1. The battery is dead or has weak power; 2. Loose or fallen wires causing switch or solenoid switch failure; 3. Worn brushes, misaligned brush surfaces, weak springs, or poor commutator contact; 4. Short circuits or open circuits in the field coil or armature coil; 5. Dirty commutator or protruding segments causing poor brush-to-commutator contact. Methods to check why the engine is not turning: 1. Inspect the starting circuit, fuses, relays, battery and connections, and the starter switch; 2. Check if the gearshift lever is in the P or N position; 3. Check the battery voltage and connections; 4. Inspect the operation of the starter's pull-in coil and hold-in coil; 5. Check if the engine's crankshaft is seized.