Sounds like you could have a faulty clutch interlock switch. Or the wire that feeds the starter solenoid is broken ...or the ignition switch itself is bad.
notice the red wire that feeds back from the solenoid to the ignition switch connector feeds through the clutch interlock (manual ) or neutral safety ( Auto )
First check to make sure that the clutch interlock switch is functioning when the clutch is depressed I have seen them not make contact and I believe there is an adjustment there.
You need to test this wire for 12v when the key is put in the START position not run. Test for 12 volts on both sides of the interlock switch with the clutch depressed, as someone tries to crank the key for you .