I have a couple simple ideas that are usually the cause. Check the backflow device and make sure the handles are inline with the pipe that each of the 2 handles are mounted on.
Check for a rainsensor, After you have checked for the rainsensor, if the cable is cut from the controller (or point of connection to the wire to the rainsensor, the system will be dead.
Of course, if these ideas don't get you started find the water tie in usually close the water meter and see if the isolation valve is closed.
Good Luck