Why won't my excavator start?

I have a Komatsu PC50 mini-excavator. My worker changed the diesel filter and now it won't start. He says the diesel isn't getting through so perhaps there are air pockets? How would I resolve this issue?

1. Loosen the fittings on the filter to purge air... 2. Lightly ether start engine... 3. Tighten fittings when leaking diesel fuel...