Q: Today's macbook air mid 2011 show horizontal line

Hello there, Fontas.

When seeing issues with internal display on your MacBook Air the following Knowledge Base article offers some thorough troubleshooting steps:

Apple computers: Troubleshooting issues with video on internal or external displays - Apple Support

If after reviewing the recommendations under "No video or no signal, image distortion, "snow," or flickering", your issue persists, then reviewing this last section would be your next step:

Helpful related articles

These articles may offer additional assistance and information about displays and video adapters:

• Apple Portables: How to use your computer in closed lid mode with an external display
• Apple Cinema Display (30-inch DVI) has 1280 x 800 as the maximum available resolution
• Mac Pro (Early 2009), Mac Pro (Mid 2010): Supported display configurations
• For assistance with Retina displays, please see Frequently asked questions about using a Retina display.

If you tried all of these steps for your display and the video issues persist, contact Apple technical support or take your Apple computer to the nearest Apple Store or Apple Authorized Service Provider (AASP) for diagnosis. If you plan to visit an Apple Retail Store, make a reservation at the Genius Bar using http://www.apple.com/retail/geniusbar/ (available in some countries only).

Note: Diagnostic fees may apply for issues not covered under warranty or the AppleCare Protection Plan (APP).

 

Thanks for participating in Apple Support Communities.

Kind Regards,

Pedro