When your clock is counting down, but no water is coming out the heads, there are a couple things that could be happening.

First and foremost check to ensure the water is ON to the system. Be sure it is turned on in the basement and both valve handles on the backflow device are open as well (going with the pipe). Check the valve boxes to be sure the drain valves are closed. If the water is on everywhere, you likely have a wiring problem or a master valve issue and need to set up a service appointment.