Ford 4500 stalled -and won't start

Hi everyone I have a Ford 4500 backhoe - 1975 I think - and I stopped to check and retie the load I was carrying and I thought it was in neutral. When I let off the clutch it stalled and then after I made sure it was in neutral it would not turn over. Batteries good, it has fuel but it will not crank. Any ideas, thanks
Bill

Ford 4500 stalled -and won't start