If it's pvc look for a clog at the last working sprinkler. The tee might be clogged on the outgoing port.
If you can't find a clog there then try running water backwards down the line. Attach the hose to one of the fittings where the non working sprinkler is. Maybe even cut the pipe and attach the hose there. You might have to ram something down the pipe to loosen the clog once you find it.
If it's poly pipe then it's probably pinched off somewhere.
Are you certain that all the sprinklers are connected to just 1 valve? Maybe two valves are wired together and one isn't working.