Originally Posted by Kiril
Try plugging in the controller.
While I want to ROFLMAO that is actually very good advice. You might want to check the cheap plug in transformer also. Many times they go dead. Most but not all controls are 24V as are the Solenoids valves. Other simple fixes are Ground wire Rain By-Pass being turned on/off. Be sure to change the Battery back up on Digital model controllers. If the system doesn't turn on at all it may be something as simple as plugging the unit in Like Kiril said.
BTW I have a 721 wire tracer I am no longer using. I will sell it rather than have it sitting in my closet taking up space.