If you're driving a John Deere LX176 riding lawn tractor and it stops moving, but the engine is still running, then the drive belt snapped or became too worn out and loose to stay tight on the driveshaft pulley under the engine. Installing a new driveshaft belt yourself takes a few tools, but it is a fairly easy process that will save you a mechanic's fee.
Park your John Deere LX175 mower and shut it off. Raise the deck height lever to the highest setting.
Unscrew the three pins bolted next to the driveshaft pulley under the lawnmower frame under the engine. Use the proper sized wrenches to remove the pins. Slip the belt off of the driveshaft pulley once you have the belt keeper pins unscrewed.
Push the deck height lever to the lowest setting.
Unscrew the four bolts holding the mower deck pulley covers on top of the two pulleys with the correct sized wrench. Remove the covers and slip the old belt off the pulleys. Slip the new belt "v" side in onto the two mower deck pulleys. Tighten the pulley covers back onto the top of the mower deck.
Raise the deck height lever to the highest setting.
Slip the new belt around the driveshaft pulley "v" side inward. Tighten the three belt keeper pins back into the frame under the lawnmower engine and around the driveshaft pulley.