Clean out and blow out with compressed air the entire fuel line and system. Clean tank. Bleed all fuel lines. Install all new filters. Fresh oil. Check glow plugs. Clean out critters. Then gently start to see if unit will turn over. Before any of this, you could remove starter and make sure the flywheel turns and the engine doesn’t need to be unstuck.
Make sure to clean out the screens in the bottom of the 3 electric fuel pumps as well. Make sure the injector pump and injectors are secure and not loose.