This happened to me several years ago. . Tractor stopped going down a hill. Mower lowered, and the held the tractor from moving. I took it out of gear, should have put it in park. I Fixed the problem. To check it, I started it by standing next to it. It started, mower raised, not holding the tractor any more, off it went down the hill to a cliff. All I could do was stand there watching my best tractor and mower go to certain death. By the grace of God it went into a small ditch part way down holding the tractor. It took a lesson like that for me to make sure the tractor is in park before starting. There may be something wrong with the starting switch. I don't think the tractor should start unless in park. This happened a few years ago, but it made me more aware of how quick things can go wrong, very fast. So pay attention out there. Stan