Ford Focus won't start up?

When my dad bought it, the diesel pump was said to be knackered, so my dad bought a new one and had it fitted. But it still won't start up. You can hear it turning over, but it won't kick in.

We tried spraying 'easy start' into it and it starts up, then as soon as it burns it off it cuts off.

Any ideas why it's not starting up?
Thanks!

Added (1). It's a 2003.
Yes, there's fuel in the tank x

Sounds like fuel is not getting through. Is there fuel in the tank?

Did you check that your getting fuel from the tank? That's called the Supply Pump. And then there should be a way to bleed air out of the pump or lines. And/or Prime the Injector Pump. What year is your car?

You likely have a busted coil.