your wireless router should allow you to switch on or off the Set Service IDentifier (SSID), it's the name of the broadcast. This name can be hidden so it's not made public.
You can hide this from the router. If it's turned off it wont show in the drop downs of an OS. You may need to browse directly to the routers interface, in which case you need the instructions for your router, likely from the manufactures website. The routers interface will likely be a web page you can navigate around in a browser.
on your host computer (the one in front of you) If you know what it should be you can try to connect by going the Wi-Fi drop down and selecting "Join Other Network..."
you will be asked for the network name and the type of password scheme.
In most cases it may be easier to reset the router to factory, then set it up, but sometimes it will blow out custom securities if you set those up so I recommend looking to see if you have anything in there before you commit to it.