A common cause of a starter not turning over is a blown fuse in the starter circuit. Broken or corroded wiring and damaged or dirty wires to the battery or the starter solenoid (or loose wires) can also prevent sufficient power from reaching the starter. It's important to inspect these components closely and ensure they're clean and properly connected before testing or replacing any parts. Additionally, if your lawn mower is equipped with a safety switch, it may need to be reset after it has been tripped due to an overload condition.