How old is the system? When did it last run normal - or as close to normal as possible? Any other major things that may have caused a problem? Lightning. Vandalism. Construction. Utilities/fiber optics installed/bored.
Are the valves not shutting off due to the controller? Or stuck solenoids? Debris in water supply maybe? There are a lot of variables that we cannot see from the interwebs.

I know you are more asking for a place to get info on this, which most of us can't help you with, but i'm just trying to find possible reasons/solutions for the problem.
When they don't turn on, are you getting power to the valve? Or are they having mechanical problems with the valves? What kind of valve? I know.... too many questions, huh?
