On my old Kubota, I had to adjust the clutch safety switch a couple of times over the years.
I got my Dad's 9N fired up. The starter would not turn. It was a bad/dirty terminal connection at the starter.
I would double check all the safety switches are working; Sitting on the seat, clutch in, tranny in neutral, PTO disengaged, brake on.
After that, I check voltages and make sure all the wire connections are bright, clean, and secure. That includes the battery cables, at both end. Give the ground connections particular attention.
Dirty grounds can cause endless frustration...