It sounds like a pressure problem at the head. there maybe a hunk of dirt that got in to the sprinkler head while you were replacing the head. You should take off the rotor look into the bottom of it wash it off and clean it as best you can. turn on the zone let the water gush out of the open hole for a few seconds. When you get back to the hole try not to let dirt get into the system and put the head back on. If the water does not have pressure coming out of the hole in a strong way then you may have dirt clogging the system at a funny pipe 90 or fitting.
Good Luck
If you are still having problems after this point you may need to replace the head with a Hunter PGP or Rainbird 5000. Dan