macOS Sierra: Troubleshoot Wi-Fi connection problems
If you’re having problems connecting to a Wi-Fi network, there are several solutions you can try.
Make sure Wi-Fi is turned on. You can use the Wi-Fi status icon
in the menu bar to turn Wi-Fi on.You may be out of range. Make sure your Mac is within range of the wireless network.
The Wi-Fi service may not be available in Network preferences.
Choose Apple menu > System Preferences, then click Network.
If Wi-Fi isn’t in the list of network connection services, click the Add button
at the bottom of the list, click the Interface pop-up menu, then choose Wi-Fi. Name the Wi-Fi service, then click Create.If you are connecting to a wireless network created by an AirPort base station or AirPort Time Capsule, restart the device by unplugging the power cord. Wait a few minutes, then plug the power cord back in. After the network is available, try connecting again.