I have a B7300 and know of only 2 or 3 safety switches that will prevent starting. (1)The HI-LOW range (Rabbit/Turtle) lever must be in Neutral, and (2) the PTO selection (Rear/Mid) lever must also be in neutral. (3?) The CLUTCH pedal also must be depressed other wise the engine will not start. Also, the FUEL CUTOFF must be pushed in and the Fuel Cock must be in the open position. If the fuel is off, the engine will crank but not run. Depending upon ambient temperature, you may or may not need to hold key in PREHEAT position for 3-10 seconds prior to starting. Generally, I use a default 2-5 seconds of PREHEAT (glo-plugs) before starting. When in colder weather, (below 50F) I will use PREHEAT from 10-20 seconds.
Other than that, I have never had an engine starting problem.