I'm pretty new to tractors myself, but based off of my mechanical experiences with other motorized equipment, if it just clicks when you try to start it, there are a couple of things it could be.
First is a weak Battery. If there is enough power to activate the selenoid, but not enough to turn the motor, it will do that. I'd hook the battery up to a charger or maybe try and jump it off another vehicle.
It is also possible that the selenoid is inop. You can check this by shorting the selenoid, or taking some heave guage wire and going from the pos. terminal on that battery to the connector on the starter motor. Be careful though, since it could shock you, or if the tractor starts up and is in gear it could run over you. That would hurt.
If thats not it, then your starter motor may be sad
. and in need of replacement. There are some nice gear reduction units out there that are much stronger than the originals and cost less. If you take it off the tractor, most auto parts stores can test it for you for free. I've found O'Reilly's to be very tractor friendly.
If you have lots of electrical power, a good selenoid, good starter, and it still refuses to turn over, your engine may be locked up. This would be super sad.
You didn't say if the tractor is stored outside, but I have, on one occasion dealt with a dozer that water went in the exhaust and filled a cylinder. Since fluids don't compress when it was attempted to start, nothing much would happen. Removing the glow plugs and cranking the engine would allow the water to escape and possibly unlock the engine, if some rain has gone down the exhaust stack and into the engine cylinder.
If you get through all of this, and nothing helps, then you may have a very serious engine problem, but regardless, let us know how it goes.
Good Luck
Tom
