Water pressure totally gone after turning off to repair
Option 1 - the valve (rarely operated) broke when operated and is not opening.

Option 2 - deposits, disturbed by closing the valve and draining the plumbing, have plugged the pipes. 

For option 2, open whatever valves are nearest the valve, or open up unions and flush out whatever glop may be there if ANY water flows - and/or run a stiff wire into the pipe (not through valves, but if opened at unions.) 

For option 1, the main valve will need to be replaced.

If there is absolutely no water flow at all, bet on option 1.