my riding mower is 6 years old, bought new. when i turn the ignition key the engine sounds as if it wants to start but doesn't seem to have enough torque. i charged the battery overnight but when i try to start mower, engine visibly turns slighly but won't kick in before constant clicking, grinding sound comes from area of ignition key. i'm totally confused. is the battery worn (battery indicator ok),does spark plug need replacing, is the starter shot? does replacing starter require professional installation?

Joseph B, August 2010