i would like some advice, as far as i have checke, these work

glow plugs
relay
fuel pump
fuel tank pump
has had a service

bad points:

has half tank, but fuel gauge reads empty all the time?

the engine turns/cranks but doesnt start. it did start after i connected battery charger to it (but battery if in working order :s) and it ran spot on. then turned it off and couldnt restart it.

also (not sure if its supposed to work like this), but as i turn the key, i can hear the fuel pump working.... but shouldnt it stop after glow plugs light goes off?.... because mine just keeps going :s

any advice please would be grateful