honda lawntractor clutch to deck drive does not turn, stalls trackor when e?

Ihave a lawn tractor honda mod. h3810, chassis #3810-5001519, motor G400-406 cm3, motor ser# G400 1361736 .
It starts ok and runs until I try to engage the deck drive. I checked the deck thoroughly, no problem, it's the clutch, which I cannot turn by hand or other wise, the pulley does not turn any time even when the motor is runnig. this is not an electric clutch. HOW do I get the thing off. I tried turning the centre nut but the only thing that turns is some disks inside the the clutch