I own two diesel MF 2300’s that are both over 17 years old, still running great. But, it does take some work
Some questions:
Does it crank normally...same speed as before?
If so, think glow plug. They do wear out and are easy to replace.
If not, think battery. Diesels take a certain crank speed to complete the fuel cycle.
Also check the sensor under the seat if it has one. I have had one fail. The 2300 won’t start if the sensor or connections are bad. I replaced the whole harness for the seat.
Edit: In fact, I got new seats for both!
Next would be the transmission neutral position sensor. First fiddle with it while you crank the engine (assuming a good battery). My have gotten sloppier and will be replaced.
Check fuel filter as well. If it has been sitting there may be blockage. Also check to see if fuel is getting to the engine. Your owner manual should tell you how. It is easy on the 2300 once you get the hang of it.
Does you JD have auto cutoff for low fluids, especially oil?
All I got!
Good luck.