There are two things that I have experienced, cause a non-start condition on my 5424 :
1) Glow plugs not working for some reason.
2) Some trapped air in the injector pump.
So back to basics :
engine needs :
Compression / ignition
and glow plugs help when cold
So far I don't think you have eliminated the air factor, and the glow plugs.
Have you checked that there is nothing blocking the air intake? Did some mice set up a nest while you were gone?
A blocked exhaust
would have the same effect as a blocked intake. Did a hose collapse?
While doing all this cranking, I hope you've had the raw water