lf,

Take it back and get a replacement. Are you matching the flow and pressure rating of the old head? Is it the same type(low flow versus std flow)? Aloha

If you were a little more specific..
What brand and part# is the head you are putting on?
Did you just dig around it and unscrew it, or did you extend the supply tubing?

Did you check to make sure that you did not cut the tubing while digging?

Are the other heads the same as what you are installing?

When you say that you removed it and there was no pressure, are you saying the hose end (with no head attached) had no pressure?
---------------------------------- Suggestion ------------

If the new head was attached and the head had no pressure... and if it is a commercial head... there should be a ring that holds the bottom and top section together, Unscrew the ring and pull out the inside piece. Turn it upside down. You should see a filter screen. Using a pair of pliers, you can grab one of the filter's "Wings" and pull it out. Clean it and reinstall. If the problem persists, and you have a good flow from the line, take the head back and get a new one.

Tom