Problem: Accidently, some friends of mine changed the display resolution of the Mac Book Air’s external display to an unsupported resolution. Everytime you close the lid, the screen went blank.
Solution: Starting in safe mode (holding shift during startup) and third-party tools did not work. Therefore try the following:
- login without the external screen attached (keep all other applications closed)
- Attach external screen, close the lid, the screen should go back blank.
- Press Alt + F1 keys (this will show up the display preferences window)
- Press Tab (moves focus to the list of available resolutions)
- Press Cursor up (changes resolution to the next available)
Now you should see the external display light up. Tested and verified on Mac OSX 10.6.