It definitely sounds like a fuel problem so you need to start at the tank and work all the way to the injectors checking to make sure that you have fuel. Are you sure that you actually have fuel in the tank? I have been aboard more than 1 boat where the fuel gauge was poorly calibrated and the boat was actually out of fuel. Next, see whether you have fuel after your lift
pump. Then check before and after your IP. Are you sure that you don't have the fuel shutoff either with a manual shutoff or the shutoff on the engine?
To loose your fuel prime, something had to happen. The possible causes are no fuel in the tank, a blockage in the fuel system, a major leak after the LP, or an air leak before the LP. Plugged fuel filters are almost always noticed first when the engine still idles fine but has no power. Given that you were idling the engine, this is unlikely unless it was really rough or something large plugged the system. If the system is plugged, it will result in fuel starvation, but no air will be introduced. I would be very hesitant to unscrew any fuel filters pre lift
pump because it will make it a lot harder to get the fuel system primed. If there is a major fuel line leak after the lift pump, you should be able to visually see the fuel flowing out. If there is an air leak before the lift pump, this is much harder to diagnose as you likely won't be able to see anything.
Check the simple stuff first like fuel in the tank and shutoffs. Good luck.