I have a Toro GT2100 Garden tractor I was mowing with it and got off the mower to move some tree limbs and when I got back on and started the mower I pushed the gas pedal and it would not move so we changed the drive belt and it still does not move. We have looked at all the pulleys to make sure belt is on right and the belt is just spinning on the pulley off the bottom of the engine and it is smoking. What to do