While mowing the blades stopped, I turned the PTO off and back on again with no results. Now when the PTO is turned on it makes an audible click and the pulley under the engine jerks, but does not turn. Engine runs great, and the belts seems to be fine. The safety switch for engine cut off under the seat seems to be working normally. Could the clutch under the engine be damaged or just worn out? The mower is about 7 years old, until now the only part that has been replaced is the starter solenoid and battery.