You'll need to give some more information. Typical usage of "crank over" means to spin the engine, but some people say "crank over" when they mean the engine is undergoing effective combustion and begins to run without a source of external power.
Has the tractor operated correctly recently? What, if anything, has changed?
If the starter isn't clicking, there is a failure to send electricity to the solenoid. Look for disconnected clutch safety switches, unhooked/corroded connections at the ignition switch, and perhaps the PTO lever in gear. (I don't know if that model has a PTO safety switch or not; I suspect it doesn't.)
If the starter clicks but the starter doesn't spin, there is insufficient contact between the main positive cable between the battery and the starter, and/or the grounding connections. Or, the starter is inoperable.
If the starter "clunks" but doesn't spin the motor, there is insufficient power (In the technical sense of volts*amps) to the starter, or there is something mechanically locking the engine in place. Ensure it is neutral everywhere and any hydraulic controls are fully down/in a free-flow position. If it still won't spin, a cylinder is full of fluid, the rings are corroded to the cylinder wall, or the engine has broken parts inside.