Clogged fuel lines, a pump not working or your fuel shutoff linkage came unhooked and it cut the fuel.
I can't remember how the linkage and shut off at the pump is connected so I don't remember if it is spring loaded to shut or if it is just an open/closed and the fuel stop literally just moves it.
I have had fuel problems in tractors that do exactly what you describe from gunk in the tank coming loose and plugging up the lines, that eventually caused the pump to go out.
see if you are getting fuel out of the pump by first cracking the bleed screw loose and cranking the tractor, if no fuel comes out you have a clog somewhere. If fuel comes out when cranking then loosen a line going to an injector on top of the pump and see if fuel comes out when you crank, if no fuel comes out you have a pump not pumping. If fuel does come out then you have injector issues but I can't imagine all thee injectors quit at the same time.
Of course it could be the pump gear, cam not opening/closing valves or something else internal to teh engine. Hope that it is a clogged line.