If your John Deere riding mower doesn't cut the grass when the deck is engaged, there is a good chance that the mower deck belt has broken or become too stretched out. Replacing the mower deck belt yourself will save you the money a mechanic would charge you for the repair. And replacing the belt yourself can easily be done in your own yard.
Shut off the John Deere riding mower. Pull the deck height lever to the highest setting.
Fit the proper sized wrench on the three pins that are screwed into the frame under the engine and next to the pulley on the engine crankshaft. These pins prevent the belt from slipping off of the pulley under the engine.
Remove the pins and slip the belt off the pulley.
Set the deck height lever to the lowest setting.
Use the proper sized wrench to unscrew the four bolts that hold each deck pulley shroud on top of the mower deck. Slip the old belt off the two deck pulleys. Slide the new belt around the pulleys so the "V" part of the belt faces toward the groove on the pulleys. Replace the deck pulley shrouds.
Raise the deck height lever. Slip the new belt around the pulley under the engine. Tighten the three pins back in around the pulley under the engine.