A few pictures would help a lot, but let's see if we can muddle our way through this. It sounds like the water splits off of your household water in the house. It would do no good to turn it off outside unless it turned off deep underground because it would freeze. This makes me suspect the valve you found inside is the one that needs to be turned on. It also makes sense that all valves should be turned on. Try that. Even if that doesn't work, nothing is harmed. I am concerned that you may not have a backflow prevention device in you system. Do you know if this system was a DIY project or if it was installed professionally? Without backflow prevention, you risk serious cross contamination of the city water supply as well as your own house water. Again, pictures can really help. It might be necessary to have a sprinkler repair person analyze your system to determine not only how to operate it, but it's safety as well.