I have a Hunter sprinkler system that controls 6 different sprinkler zones and keeps both my front and back yard nice and green. I have it programmed to start at 4:15 a.m. when my family is sound asleep, and it finishes cycling through the various zones at around 5:30. This morning however, I noticed the sprinklers hadn't turned on, so I opened the case of my main controller panel and saw that it was flashing "NO AC".
After looking at the owner's manual, I found out that "NO AC" means that it's not getting power and is running on it's backup battery. So I followed the cord to where it was plugged into the wall, and noticed that it had a GFI test/reset plugin installed.
Removing the "NO AC" message was as simple as pushing the button on the electrical outlet in the wall, to reset the line.
If you don't have power to the electrical outlet, check all of your wall switches, timers, or power strips that might be connected to the outlet.
You might also need to have an electrician check your GFI breaker if this tip doesn't restore power to the sprinkler unit.