If it's the brush type (I bet it is), then the rotor coil may need to be re-energised after prolonged storage.
Perform all the usual continuity checks (to ensure all the coils, breakers, etc. are measured fine and no opens/shorts) and then re-energise the coil with a 6V lantern battery.
Doesn't take much: just touch it for a few secs and then start spinning and see if you get 120AC output.
Q.