"1 - Possibly the neutral safe
"1 - Possibly the neutral safety switch is slightly out of adjustment.... jiggle the control handle slightly forward and backwards. If the engine attempts to crank over, this is the problem.
2 - There is a main fuse in one of the smaller red lines at the starter solenoid, about three inches away from the solenoid. This fuse may have blown for some reason (it happens).
3 - The lead at the "S" (solenoid) terminal of the ignition switch may be loose or broken at some point.
4 - The starter solenoid ground, leading from the solenoid to the powerhead, may be loose/dirty/broken. Also the solenoid may be faulty.
5 - Finally, and hopefully not, the starter may have failed."