Cannot get my new deep well water convertible jet pump to prime?

my well is 72 ft. deep, approx. 40 years old. have been using shallow well pumps,3/4 hp., the whole time with great results. Lawn sprinkler repair man replaced with convertible deep well jet pump, also he installed "short" venturi tube into ejector. {shallow well pump bit dust during freeze, not winterized properly}. We cannot get pump to pick up prime. I have filled 72 ft. pipe full of water and filled primer plug hole with water, I can place hand over pipe and feel strong suction when pump is running, so i feel like pump is providing good negative pressure to system...but prime will not pick up. Pump motor is set to correct watt/amp of 115. Air tank is new with pressure set at 18 lbs., pressure switch is 20-40psi {basically irrelevent at this point} Things I'm not sure of: 1- If well ran dry 2-If pipe has deteriorated/has a hole. 3- what is at bottom of 40 yo pipe...footvalve? screen? ect. 4- if well collapsed {won't prime, so don't know if sediment is present.What should I do at this point? Well is only used for lawn sprinkler system. House is on city water. Only 1 pipe exits ground going to pump with one inline brand new brass check valve. Repairman suggests installing pvc pipe down inside steel pipe {72 ft.} at a cost of $300.00 bucks. I figure water should be located first. I live in Tidewater, Va., and I believe we are in some form of a drought, we are 7 inches shy of water according to news orgs. Any suggestions or information will be greatly appreciated.