You haven't mentioned how this all started...
It would be pretty rare for the timing to change significantly without some obvious reason; loose sprockets, loose mounts, damaged belt...
More often, an engine that won't start isn't getting fuel to the injectors or has low compression. Crank the engine with an injector tube loosened and see if fuel leaks from it.
If there is fuel getting to the injectors, check the preheaters: Are they getting power during the preheat stage? Do they all heat? You can test them individually with an ohmmeter and compare.
If you are getting fuel and preheat, you can try to increase the compression for starting: Remove the front rubber boot from the intake manifold and squirt engine oil in, trying to reach as many cylinders as you can (don't inject enough oil to cause hydraulic lock). The oil helps the rings to seal, and as it occupies space in the combustion chamber it increases the compression ratio. I ran a worn-out NA Volvo for several months that way; it lacked power but otherwise ran fine. I usually only had to oil it first thing in the morning; the rest of the day it started OK.
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