Back up all data before proceeding.
Sometimes the Wi-Fi icon in the menu bar may falsely indicate that Wi-Fi is unavailable. That could happen if you switch between network locations, one of which doesn't have a Wi-Fi service.
Open the Network pane in System Preferences. If there is a closed padlock icon in the lower left corner of the preference pane, click it and enter your administrator password to unlock the settings.
A list of available network services appears on the left. If Wi-Fi is in the list, select it, then from the popup menu labeled with a gear icon at the bottom of the list, select
Make Service Active
Click Apply.
If Wi-Fi is not in the service list, click the plus-sign button at the bottom of the list, and then select Wi-Fi from the Interface menu in the sheet that drops down. Click Create, then Apply.
If the above steps don't solve the problem, continue.
Triple-click anywhere in the line below on this page to select it:
/Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist
Right-click or control-click the line and select
Services ▹ Reveal in Finder (or just Reveal)
from the contextual menu.* A folder should open with "com.apple.airport.preferences.plist" selected. Move the selected item to the Trash. You may be prompted for your administrator password. Restart the computer and recreate your settings for Wi-Fi in the Network preference pane.
*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select
Go ▹ Go to Folder...
from the menu bar and paste into the box that opens by pressing command-V. You may not see what you pasted because a line break is included. Press return.
