MacBook Air (Mid 2011) shows a black screen after trying to install EFI Update 2.9
Follow these steps if your MacBook Air (Mid 2011) doesn’t finish the EFI Update 2.9 firmware installation, and a black screen appears after the computer restarts.
This article has been archived and is no longer updated by Apple.
Make sure your MagSafe power adapter is plugged in to a power source and connected to your MacBook Air.
Press the power key for at least ten seconds.
Release the power key.
Press the power key again to turn on your MacBook Air.
Your MacBook Air may take a few minutes to power on.