re: OT Plumbers - quick questions

off hand i would say there is trash in the line blocking the valve.

turn off water, remove valve, check for trash in the line and blow through the valve both ways to be sure its clear.

i have seen the seat from old valves come off the handle and stay stuck blocking the flow, i have also seen shite from construction in the lines for years then just by chance one day it works its way to the valve and causes a blockage