What are the circumstances in which it broke down?? Did customer just start it up from cold,moved it off drive or something then switch it off maybe went out next day or later then non start ?? I'm thinking simple bore wash ,pull plugs out put drop of oil down bores,disconnect injectors or remove fuel pump relay,crank over a bit refit plugs then wind over with foot flat down till it goes when it starts firing keep starter in till it catches,once running hold at fast idle till warm then road test,job done

If that doesn't work do as Jon says check cam timing.

Matt