Dave is heading you down the right direction he, but I would try one thing different first. On the right side loosen the bolt that attaches the fuel lines to the side of the fuel injection pump, turn the key to the on position and you should hear the fuel pump ticking. When fuel comes out at your loosened fitting tighten the bolt and try to start the tractor. You could also check the fuel for gasoline or water at this point. If that doesn't work, move on to Dave's suggestion to see if you are getting fuel at the injectors, and then on to the glow plugs. If your fuel system has lost its prime, loosening the fuel line process will reprime the system. Good luck and let us know.