See answer to other chaps question about glow plugs etc.
(1) Tilt the cab (if you have never had to do this don't be afraid to ask!)
(2) Operate the thermostart from the cab and then see if you can feel heat radiating from around the thermostart unit (manifold heater) on the inlet manifold. If there's no heat coming from it, it is either not getting fuel in which case there may be some heat- due only to the electrical element or not getting electrical supply - or both. Check wiring and fuses. Otherwise it could need to be replaced.
JD
January 2008