I have an old tractor, an it stop working.
I thought it needed a new battery so I bought one, but it still does not want to start.
All I hear when I turn the ignition switch is a clicking sound but he motor will not turn over.
What do I do?

First try to turn the engine over by hand to ensure that the engine is not seized. If the engine is not seized then you have a bad solenoid or starter. The solenoid is the part bolted to the starter that is about the size of a D cell battery that the wires bolt to. Remove the starter and take it to an authorized serviced center and they will check it for you for free. They will also be able to determine if it is the solenoid (relatively cheap) or the starter (relatively expensive).

If you have a friend that is a mechanic, you can ask him or her if they would mind trying to "jump" you solenoid. They can do this with a screwdriver (if they know what they are doing). This will also diagnose it (i.e. if it can be jumped it is the solenoid that is bad, if it can't be jumped it is the starter)

IF THIS ANSWER HELPED YOU PLEASE RATE IT.

Could be the solenoid.