my largo wont start

i have a 1995 nissan largo 2l diesel, i bought it 6 months ago and it worked perfectly but it has been stood for the majority of that time and it wont start. i have taken the battery out and charged it and also tried jump starting it from another vehicle but it still wont start. the starter motor is trying to start the engine but it just wont happen. any thoughts? any help would be greatly appreciated thank you sorrel.