Our water pressure suddenly went to zero. Everything seems to be working properly, but I have to reset pump to get it to kick in, and it runs for a short while to about 50 PSI. No water is filling the pressure tank, though some flow to house. In about 5 minutes the water pressure is gone, and there i8s no water.

Do you have to prime the pump before it begins to pump water?
By "pressure tank" do you mean a bladder or a galvanized pressure tank? (see images) If a bladder tank what's the PSI charging the tank? It should be 2 PSI under the cut in point of the control box. Do you get 50 pounds of pressure to the house before the pressure drops off? It sounds as though you have a leak either in the line going to the house or a hidden leak in the house itself, Are you on a slab? Please answer my questions and I'll answer as soon as I can. Regards, Tom