is it getting fuel. are all your safety devices working. do you have the manuals for it.you can get some good help on here but they need to know exactly what preluded to this. so sit down and start from the beginning of what happened and what you did,Without knowing why the injector system was replaced, this is all just wild speculation...
Does the engine have good compression on all cylinders?
Is the fuel pump delivering fuel to the injector pump?
Some engines require complete bleeding of all the air in the fuel lines up to the injectors, this might be one of them.
Like any engine, the timing has to be correct. The injector pump has an adjustment range just like a distributor on a gas engine, if the timing is off it won't start.