It’s not the computers where you should be looking; the easiest place to find your settings including the WEP or WPA key (“password”) is the router. Which may itself have a login password, hopefully you have that, then just navigate to the the wireless settings.
ETA: And the router itself is usually accessed through its web service at a specific local IP address, often something like 192.168.1.1, but different brands and models differ.
Write the password on a piece of tape and afix to the bottom of the router once you figure it out. If you can’t determine the the existing password, there’s usually a reset button to knock the router settings back to factory default.
Most current routers also should support WPS, so that you don’t need to enter a password at all. When the password prompt appears, you can instead just push the WPS button on the router (depending on the model, a couple of seconds or until some light flashes or similar), and the connection will be set up automatically.
Some routers include a small, hard-to-press button that will reset the router to its factory default SSID and password (e.g. “admin”), which are typically noted on its label, or can be found via an online search of the router model ID.
Note that using this scheme will require resetting devices that are currently connecting using the now-forgotten password.