1st step - With the injector line disconnected, crank the engine around. You should see fuel spurting from the end of the injector line. If not - there's either air in them, or you need to look at the injection pump. If you see a decent gob of fuel every firing stroke, move on to step 2.
Step 2: With the injector removed from the engine, re-connect it to the fuel lines. Crank engine over (keep your hands well away from the injection end - if it's working, it can actually inject diesel fuel through skin - nasty!). You should see a nice fine mist of fuel. If you see fuel but it's not well atomised, your injectors need servicing/replacing. If no fuel comes out, then either the injector is jammed, or the pump is too weak.
If your pump isn't pumping, it may be seized, or it may be worn. I don't know if you can easily see the IP (Injection Pump) operating on the LD engines, I suspect not... so you may need to pull it to have a look. If it's seized, then the pump won't be returning when the cam has passed the follower. If it's worn, then the follower will be down, but the fuel is going down the sides of the piston instead of up the pipe. Pumps can be repaired, but they're extremely fine tolerance devices, so it might be easier/cheaper to get a 2nd hand one.