Sounds like one of those "fun" ones

If you can't get at ANYTHING on the engine, you about need to use a forklift or something to get that box up an out of the way. I run into the same problem on some skid steers, but there is an extra port on the lift cylinders, I just connect a hose there and to another tractor, etc and lift the boom out of the way, with a hydraulic remote. I would think they have some sort of provision for getting that box out of the way, but maybe not.
If there is no smoke, I bet it is out of fuel (did you check that FIRST?

) or the system is airlocked. If it has been sitting in storage all winter, I be the fuel leaked back out of the system. Loosen the bleed port on the filter head or the line at the injection pump and either crank (mechanical fuel lift pump) or turn the key on (electric) till you got a good STREAM of fuel. Then give it a shot.
If it IS smoking when you try to start, maybe try some ETHER (oops) and see if you get any life out of it.
Oh, I missed that you already tried that.
Did you check the air filter? If it is plugged tight, diesels start kinda hard.
Let me know what you find...-popcorn