MacBook Air display went haywire
Press the power button to turn on your computer.

Press and hold the D key before the gray startup screen appears.
It takes a minute or so for AHT to start up and inspect your hardware configuration. 
While this is taking place, an icon appears on the screen.
When the process is complete, select US language and click the right arrow. 

You can also use the up and down arrows to select a language and then press the Return key.

The AHT console appears. You can choose which sort of test or tests to perform:


To perform all of the basic tests, click the Test button or press the T key or the Return key.
To perform a more thorough diagnostic test, select the "Perform extended testing" checkbox under the Test button before you click the Test button.
Note: Your test results will appear in the window in the bottom-right of the console.
To exit AHT, click Restart or Shut Down at the bottom of the window.


Dropping the Mac also bends the graphics card out of place.