You've given us very little information to go on, but here's some place to start. Solenoids are connected to the controller with wires. Follow the wires from the controller. In a perfect world, the solenoids and their valves would be in a box quite close to the controller, but with a homeowner-designed and installed system all bets are off. If you can determine the direction the wires are headed and use some reasoning, you may be able to use a probe and find the box. There should be no water flowing in a sprinkler line if the solenoids are functioning correctly. The only time there is water in those lines is when the controller tells the solenoid to open the valve, so I would suspect a fault solenoid or perhaps a valve. If you live where it freezes in the winter, it is possible the system was not properly winterized and the damage may be freeze related. With everything hidden, if you can't find the solenoids fairly easily and quickly, it might be wise to get a professional sprinkler company to come in, locate everything, make sure it is properly repaired and operational, and give you some pointers on the care and feeding of the system. I should not be necessary to dig up the entire lawn.