Before you check your glow plugs, on your first start in the morning, have the bonnet up ready, turn the ignition on and check the clear plastic pipe between the fuel filter and the injector pump. If you see bubbles of air, fuel is running back. Also, a tell tale sign of this is that you'll get one quick crack of the engine as it uses the fuel in the pump, then it will stop and you'll have to wind it over and over - almost to the point of flattening the battery.
If this is the problem, check the leak off pipes on top of the injectors. Also, the very last one against the bulk head has a rubber blanking cap, very prone to splitting. You'll know which injector is causing the problem cos it will be damp around it. Also, number 4 has a wire coming out (expensive one!). This tends to leak around the wire.
Happy searching and good luck!