Okay you must be posting from a phone or your browser correction butchered your post.
Let me see if I understand you correctly
Last night you were mowing, while mowing you went from forward to reverse and your mower dies?
So you think your tranny is stuck between drive and reverse thus not allowing you to start your mower?
Now if you have a newer D170 and if I am not mistaking, when you go into reverse with your mower it will kill the engine unless you shut off the mower deck, so have you shut off your mower deck, push your e-brake, and tried to start it?