How does the range lever feel? Do you feel detented positions for the A-B-C ranges and neutral? The neutral safety switch is incorporated into the forward and reverse pedals. If you push one of the pedals, it should not start. How about the seat safety switch. If it is not working, it will not move. I have seen some seats "freeze" in cold weather and the cushion does not flex enough to activate switch. I have also seen some "light" operators have trouble activating the switch sometimes. If all that checks out, you probably have either a loose wire or a sensor that is bad or needs adjustment.