Most likely stuck pumping plungers but could be stuck metering valve. I personally would put my gauge on and check for primary fuel pressure and go from there. You can easily take top off pump and see if throttle moves the metering valve and if it doesn't a finger gently push it up and down and back and forth.
No way to see pumping plungers sooooo, a few raps on the solid portion of pump with a soft hammer might just jar them loose if you are really lucky. Other wise, it is tear down time.