Update your software and firmware
Many common display issues can be resolved easily by making sure the software on your Apple computer and the firmware on your video adapter, display and Thunderbolt cabling is up to date. Check for updates for Apple products by using Software Update, the Mac App Store, or visiting Apple downloads. Check with the manufacturer for any updates that may be available for displays, extenders, or adapters not made by Apple.
It is very important to have the proper operating system installed for your Apple computer. Confirm what version of OS X originally came with your computer here, and confirm which version you are using by choosing About this Mac from the Apple () menu. Be sure you have that version or a later version installed for optimal display operation.
Should issues persist after updating, follow the steps below to troubleshoot these issues:
No video or no signal, image distortion, "snow," or flickering
When using an external display be sure to check the following:
- If you're using an Apple notebook, confirm the AC power cable or adapter is securely connected to the computer and the cable providing power to the display is also secure. It is always good to have your notebook connected to AC power when an external display is in use.
- Confirm display adapters are fully seated in their respective connections and that they are supported models and for the computer and display. Refer to these articles to assist you with adapter compatibility and further configuration information:
- Remove all display cable extenders, KVM switches, or other like devices and retest to determine if the issue is resolved.
- Try unplugging the video adapter or cable and then plug it back in.
- If more than one video adapter is in use (or "daisy-chained"), troubleshoot by using only one adapter.
- Example: A mini DisplayPort to DVI adapter connected to a DVI to HDMI adapter is an unsupported configuration because there is a series of adapters in use.
- If available, try using a different display and or adapter (or use a different connector by using DVI instead of VGA, for instance).
Reset the system
Reset the resolution
Start by resetting the Mac's parameter RAM. If the display does not come up, was previously set to an unsupported resolution, and still results in no video:
- Start up in Safe Mode.
- From the Apple () menu, choose System Preferences.
- Choose Displays from the View menu to open the preferences pane.
- Select any resolution and refresh rate that your display supports.
- Restart your computer.
Using Closed lid, Extended Desktop, or Mirroring display modes
When using multiple displays, information can be presented in a number of ways. For more information and what modes are supported by your Apple product refer to:
Brightness or color isn't uniform
If you have an older display, before evaluating the display for uniformity in lighting or color, the display may need to warm up. Older LCD (Liquid Crystal Displays) use CCFL (Cold Cathode Florescent) backlights. This kind of lighting may require several minutes to half an hour to warm up fully. CCFL backlit displays include the Apple Cinema Displays (20-inch DVI), (23-inch DVI), (30-inch DVI).
Newer displays use LED (Light Emitting Diode) backlighting that can achieve full brightness and color saturation almost immediately. An example of an LED backlit display is the Apple Thunderbolt Display (27-inch).
If you continue to have issues with brightness or color uniformity, check the Displays System Preferences pane. Choose System Preferences from the Apple () menu, then choose Displays from the View menu. From the preference pane you can adjust brightness on internal and Apple external displays on the Displays Tab, and calibrate your display from the Color tab.
Note: Third-party displays may have brightness and additional color adjustments available on the display itself.
When using a monitor via an HDMI connection, you may notice poor video quality if your display is set to television mode. Switch to monitor mode to achieve the best video quality. Check the documentation that came with your display in order to switch to monitor mode, or contact the manufacturer for assistance.
If you have concerns about pixel anomalies, refer to these articles for more information:
Display is unusable after changing to an unsupported resolution
If you experience a black screen, or otherwise have an unusable picture after changing to some resolutions, try resetting the NVRAM first.
If you continue to experience the issue, startup the Mac in Safe Mode. Delete the /Library/Preferences/com.apple.windowserver.plist file and restart the Mac.
How do I select additional resolutions on my display?
You can use the Display pane of System Preferences to specify how your display works. Not all options appear for all display models. By default the best resolution for your display will already be selected in System Preferences.
To select a different resolution, use the Scaled option. Some additional resolutions may be available when you hold the Option button.
How do I use AirPlay mirroring?
AirPlay Mirroring (if your Mac supports it) allows you to show your Mac's screen on your HDTV via an Apple TV (2nd or 3rd generation). This option doesn't appear on Macs that do not support AirPlay mirroring.
How can I detect displays?
If the detect displays option is not available, hold down the Option key while you are in the Display pane.
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).