When a sprinkler valve is not turning on, it can be an electrical problem or a water supply issue. A good place to start is by ruling out a water supply problem. To do this check the other sprinkler valves to ensure they are getting water and turning on.

If none of the valves are turning on then look for the water shut off valve to the sprinklers. It could be that the water source is turned off and just needs to be turned back on.

If only one valve is not turning on, check to see if it will turn on manually. When the valve works if started manually the problem is likely with the solenoid or the wires.

Start by checking the wires first. Make sure there is good contact where the wires connect. Check that there are no cuts or breaks in the wires. If the wires look fine it could be the solenoid. When the wires are damaged the best option may be to replace the solenoid completely anyway. But if the wires are just loose it may be possible to reattach them.