If you can’t choose a Wi-Fi network
If you can’t choose a Wi-Fi network, check your network connection, cables, and your base station.
If you can’t see your Wi-Fi network: Check that Wi-Fi is enabled on your Mac. Choose Apple menu > System Preferences, then click Network. If it isn’t, click the Add button , click the Interface pop-up menu, then click Wi-Fi. Give the Wi-Fi service a name, click Create, then click Apply.
If you can see your Wi-Fi network but can’t connect to it: Your signal may be intermittently compromised by a source of radio frequency interference, such as a microwave oven. Try moving your Mac closer to the base station, and then see if you can connect to your W-Fi network.
See Items that can interfere with a Wi-Fi network and the Apple Support article Potential sources of Wi-Fi and Bluetooth interference.
Verify that the router is connected and working properly: Remove the router’s battery and power supply and restart it.
Restart your base station: Unplug the power cord and plug it in again, then try reconnecting. Verify that all the cables are connected to the base station.
If the amber light on your base station is flashing: See If your base station’s light is flashing.
Reset your base station: This restores your base station to a state where you gain control. You might want to do this if, for example, you forget your password or the device is not responding as expected. See the Apple Support article Resetting an AirPort base station FAQ.
To reset your base station to Apple factory settings, use the instructions in Erase and restore your base station or Time Capsule before giving it away.