I find that, if I'm not careful, I can snag my clothing on the PTO or shifter levers getting in or out, and not know it. Just enought to jog them off the detents. Caused some ???!!'s to sprout out of my head one day.
I have had a similar problem with my B2910. The safety kill switch will sometimes stick. With my unit it is the one which works off the forward hydro pedal. When I kick the pedal in a couple of times it usually releases and then the tractor starts up fine. Also try kicking the break pedals hard. I fixed the problem by adjusting the switch which is located under the tractor about half way back from the front edge of the seat on the right side as you sit in the seat.