I have an MTD Lawn Tractor Model 13AN690G352 I bought secondhand recently. I don't know how old it is. It starts OK and it operated OK for the first hour or so. I stopped it to take a phone call. It then restarted OK, the cutting deck was able to be raised and lowered and the blades were able to be engaged and disengaged OK. However, no matter what I do with the Hydrostatic Control Lever, I can't get the tractor to go forward or back again.