New to sprinkler systems

We moved into our new house (new to us, that is; the first one we've ever occupied that has a sprinkler system) in November, and the sprinkler system had already been winterized.
Today I decided to check it out. I opened the two valves, one either side of a brass/bronze gizmo (more or less conical in shape) with a black plastic cap, and I could hear water flowing, but most of the heads are merely dribbling water and not distributing it over a wide area. The exception is a point where the head seems to be totally missing, with the water shooting straight out of the ground; even when I plug this one, however, the water flow from the others does not change significantly.
I turned off the two valves, then turned them on again, but now water is pouring out from under the plastic cap of the aforementioned brass/bronze gizmo.
Is there anything I can do myself to fix the system (obviously I can install a new head to replace the missing one), or am I stuck with calling in a maintenance company?
It's a basic system -- manual (no timer/controller) with only one zone. We're in W. Michigan.
MB
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significantly.
If it were me, I'd call the outfit that winterized it & have them come out and turn it on. Make a point to be there & watch what they do to get it back in service. Next spring you can do it yourself. (you will still need them to winterize it)
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A drain valve is open or it wasnt winterised right.
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The anti sphion valve froze and is leaking. There are repair kits for most.
Tom

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