My Peugeot 806 2.0 HDi has just stopped and will not start ,?

My Peaugeot 806 has just stopped working and will not start , I braked quite hard and that was that it will not go.
Have put new heater plugs , there is no diesel coming through the pipes and I cannot here the diesel pump working when I turn the power on . I am loathe to buy and fit a new pump in case it is something else ie the immobilizer .
can anyone suggest a cure ?