MacBook Pro problem

Try Intel-based Macs: Resetting the System Management Controller (SMC).

Take it to the Genius Bar.

I'd normally interpret an X as meaning either that a WiFi card is not installed or the card that is installed is disconnected or defective. If you check the System Information app (hold down the option key when you click the Apple menu, it should be the first option), look down under Network/WiFI; see what it says about the card under the Interfaces section (en1). The Genius Bar can do tests, and if necessary ship your machine back to Apple for repairs.

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.