Make sure that your display's power cable and video cable are connected securely and correctly at both ends. Learn more about how to connect a display to your Mac.
If you're using an adapter with your video cable, the adapter must support your display's resolution and refresh rate. Thunderbolt and USB-C adapters must also be compliant with DisplayPort Alt Mode, Thunderbolt 3, or Thunderbolt 4. If you're not sure about your adapter, try a different adapter or replace the video cable with one that doesn't require an adapter.
If the display is connected to a Mac laptop computer with a closed lid, make sure that the Mac is connected to power and using an external keyboard and mouse.
Find out what your Mac supports
Your display will be dark if it exceeds the maximum number of displays that your Mac can use at the same time. This limit varies by Mac model.
Your display will be dark or use a lower resolution or refresh rate if you configure it to exceed the maximum resolution or refresh rate that your Mac can use. These limits vary by Mac model, and by the resolution and refresh rate of other connected displays.
To find out how many displays you can connect, and at which resolutions and refresh rates, check the specifications for your Mac model:
Detect your display
If your Mac can't detect your display, your display will be dark. Use one or more of these steps to try again to detect your display.
- Disconnect the display from your Mac, then reconnect it. It might help to turn off the display first.
- Put your Mac to sleep, then wake it. On Mac laptop computers, you can close the lid for a few seconds, then open the lid again.
- Choose Apple menu > System Settings (or System Preferences), then click Displays. Press and hold the Option key to show the Detect Displays button, then click the button.
- Restart your Mac. If you can't restart your Mac, press and hold its power button for about 10 seconds to turn it off. Then press and release the power button to turn it back on.
Allow your display to connect
Check display brightness
If your display is dark, make sure that its brightness hasn't been turned down.
- If your keyboard and external display are made by Apple, you can use the Brightness Up key on the keyboard to increase brightness. Or choose Apple menu > System Settings (or System Preferences), then click Displays and use the brightness control there.
- If your external display is not made by Apple, you might need to use its built-in controls and menu system to adjust brightness. If you can't do that and your display is dark, the display might not have power, or it might be malfunctioning.
Software can affect display detection, the quality of the image on your display, and the resolutions and refresh rates available to your display.
- Install the latest macOS updates, which also deliver firmware updates for displays made by Apple.
- If your display is not made by Apple, make sure that it's using the latest firmware from the manufacturer. Check your display's documentation or the manufacturer's website for details.
- If you're not sure that your Mac is turning on or starting up, learn what to do if your Mac doesn't turn on.
- If the display is working but its picture seems blurry, try using a different resolution. The display's default, native resolution might be sharper than a scaled resolution. Some third-party displays have built-in controls that you can use to adjust picture sharpness.
If you still need help, contact Apple Support.