Troubleshooting guide
How to fix the problem
Check adapter compatibility, cable and monitor Input; System Settings > Displays. Not every Mac model supports multiple external displays.
Possible solutions
Choose the method that matches your situation. Start with the simplest suitable option and check the result. If the problem is fixed, you do not need to continue with the other methods.
Direct screen connection
Try a single monitor without a dock, selecting the correct input and cable.
Steps to follow
- Check that the monitor is turned on and that it is possible to open its own menu with the buttons on the body.
- In the monitor's Source/Input menu, select the exact jack that the cable is connected to, such as HDMI 1 or DisplayPort.
- Turn off the computer and display, reconnect the cable firmly at both ends, bypassing the dock or hub if possible.
- Turn it on and check the image. If not, after disconnecting the power, try another suitable cable and, if you have one, another screen.
Checking adapter and Mac limits
Compare other compatible adapter and model number of screens and mode support.
Steps to follow
- Write down the exact Mac model, adapter and monitor.
- Check the Apple model description for the supported number of external displays, resolution, frequency and cover mode.
- Test a single display directly, with the correct cable and Input, bypassing the dock.
- If one works, the problem may be with the dock or support for a specific multi-screen configuration, not a macOS bug per se.
If the problem persists
Connect one monitor directly without a dock and check its input. If the display works on another computer, check the adapter and Mac supported mode; the total number of screens depends on the model.
Request a repair