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As above I'd check for water in the diesel filter... there's a drain at the bottom.
Then bleed the fuel system all again.
A compression/ leakdown test will show up any problems with head gasket and piston rings, but I think that's unlikely.
Next would be set the valves...they do wear. I'm not sure how far out they'd have to be for a no-start though.
Again, check the fuel solenoid at the injector pump. You can hotwire this if needed.
Put a hot wire to the spade lug and feel for a "click" - then make sure the OEM wiring has voltage when the key is "ON"
When cranking you should be seeing a good squirt of diesel at the injector nuts when they're loosened slightly.
Beyond that unfortunately sounds like computer/auto issue which is where I run out of knowledge :/