Question
One of our zones is not operating, my husband removed the grass that grew over the sprinkler heads and all popped up and worked great.  The next morning he went turn it on and nothing.  He checked and water is flowing through the system at a very, very low pressure.  Why was it working great in the evening and the next morning nothing, he didn't do anything in between? thoughts on what he should take a look at...

Answer
Could be a couple of things.  I would suspect that since some work was done around the sprinkler heads there may have been some inadvertant damage and you now have a leak or broken sprinkler or the pipe under the soil.  Poke around each head with a shovel or other tool with the water turned on and see if there isnt some evidence of a leak.