JD 145 transmission problems?

I have a JD series 100 garden tractor that suddenly stopped working today. The drive belt came off. I put it back on and everything seems to work fine but it still doesn't go. The free wheel lever is all the way in. All of the switches and levers are connected. The drive belt turns the auto transmission pully but it still will not go when you step on the forward or reverse pedal. It is not making any strange noises.