I very much doubt the cable is the problem because with these the clutch is always disengaged until the cable is put under tension. This indicates something is wrong in the gearbox or the axle has locked up in the bushes, but this is unlikely. As Speedy said, remove the belt and the gears in each wheel and it will be a good push mower and once you remove the belt you can start on getting the motor running. You can't with the belt on and gearbox locked up
