Common rail diesels such as yours are not dependant on glow plugs for cold starting. The purpose of the glow plugs is to reduce engine noise when cold and to provide better running during warm up. However they do switch on for pre-heating when the outside air temperature is very low. I would get it hooked up to a scan tool and check the fuel rail pressure when cranking. This must achieve at least 10,000kpa when cranking otherwise the engine will not start. Also at the same time check to see if the ECU is receiving a good RPM signal from the crankshaft sensor......

Railroad thanks for the responce, would these issues not be stored as fault codes though?

Also if it was these problems would the problem not be there all the time?

No, not necessarily. The ECU monitors fuel rail pressure via a sensor in the rail itself, and controls a pressure relief valve which will either be located in the rail or in the pump. A code will be stored if these components were to go either short or open circuit, or if the programmed parameters were exceeded for a certain period of time. A code would not necessarily be stored if the rail pressure were low for a brief period, but the engine would not start for that time. If the rail pressure is low you will need to look into the reasons why so you do need to know what the fuel rail pressure is. Unless you do know that there's not much further you can go without guesswork. Similarly you can fiddle all you like but if you don't have an engine RPM signal the engine isn't going to start, and you can't tell just by guessing.

The ECU needs an engine RPM signal from the crankshaft sensor. It also needs a signal from the camshaft sensor for cylinder identification. There is no need for the high pressure pump to be timed to the engine, but the pressure in the fuel rail should increase quickly when the engine is cranked and reach 10,000kpa and more. When this pressure is reached the ECU will switch the fuel injectors by capacitor discharge. At this point the engine should start.

When you crank the engine do you see white smoke puffing from the exhaust? Fuel is being injected if you do, so that is one easy check you can do yourself.