2000 Citroen Xsara 2.0 HDi won't start please help

My Citroen Xsara had been running fine even up until last night. Today it just won't start, brand new battery 3 weeks ago. Turns over but just won't fire, getting diesel upto the injectors. Even with easystart it tries to fire but won't run. AA been out and left scratching their head. Maybe imobiliser problem although light not on on dash and keyfob works fine. Also mentioned it could be the cam sensor. Computer records 300 bar at fuel rail and rpm ok. Could this be heater plugs or would it have started with easystart if this was the case? It's driving me mad any help appreciated.

is this equipped with glow plugs or has it got an intake air heater? if its glow plugs use a test lite to determine if power to glow plugs.if you have power to the glow plugs you should check each plug to see if its working.a quick way to do this is to disconnect the power wire from each glow plug.then take a test lite and connect one end to the pos battery terminal(assuming this vehicle is neg ground).take the other end and touch it to the terminal end of the plug.if the lite lites up the plug is ok.dont know what your level of mechanical ability is so if you need clarification please post back.

Thanks Aldan, I'll check that out today along with the cam sensor.