Sprinkler Fail

After putting one more coat of paint on the door, I took my old DirecTV dish and removed the actual dish from the arm, intending to use the dish to block sprinker spashback from hitting the gazebo. However, I soon discovered that none of the sprinklers in the back yard would turn on. So I tried the front yard, and they worked, but noticed that one was not popping up because it had become overgrown with grass roots, and another had significant bubbling coming from its base. Clipping free the overgrown one was simple enough, but digging out an area around the other proved to be quite difficult with a bunch of roots in the way, including a couple big tree ones. After hacking away with the back of a hammer for a bit, I eventually got out the chainsaw to take care of the thick ones. That sprinkler was located just outside the grass, in a rocky area, which also made it difficult to dig up but at least I didn't have to destroy the lawn doing it. A quick trip to the hardware store for a little plastic replacement piece was all I needed to get it back in shape. But still haven't figured out why the backyard sprinklers seem dead.