How to Fix an External Display Not Detected on Mac

Resolve connection issues between your Mac and an external monitor. Follow these steps to verify cables, refresh display settings, and reset macOS drivers.

1. Verify physical connection and power. Ensure the external display is connected to a power outlet and powered on. Disconnect the video cable from both the Mac and the monitor, then firmly reconnect them to ensure a secure seating. If using a hub or docking station, bypass it by connecting the display directly to the Mac to rule out hardware failure in the adapter.
2. Force the Mac to detect the display. Open System Settings from the Apple menu. Navigate to Displays, then hold the Option key on your keyboard. A Detect Displays button will appear in the bottom right corner of the window. Click this button to force the operating system to scan for connected hardware.
3. Modify refresh rate and resolution. Within the Displays settings menu, select the external monitor if it appears in the diagram. Check the Refresh Rate dropdown and select a lower value, such as 60Hz. If the resolution is set to an unsupported mode, toggle it to Default to reset the signal to a standard frequency.
4. Restart the WindowServer process. Open Activity Monitor from Applications > Utilities. Type WindowServer into the search field at the top right. Select the process, click the X icon in the toolbar, and choose Force Quit. This restarts the graphics management process without requiring a full system reboot.
5. Perform a Safe Mode restart. Shut down your Mac completely. For Apple Silicon Macs, press and hold the power button until 'Loading startup options' appears, select your disk, hold the Shift key, and click Continue in Safe Mode. This clears system caches and disables third-party display drivers that may be interfering with the connection.