Try these steps in order until the third screen is detected again:
- Check basic connections and hardware
- Disconnect all accessories (docks, dongles, adapters) from the PC.
- Reseat the video cable for the 3rd monitor at both ends.
- Try a different cable for that monitor.
- Test the 3rd monitor on another PC to confirm it works.
- If the PC has multiple video ports (HDMI, DisplayPort, etc.), plug the 3rd monitor into a different port.
- Confirm Windows display settings
- Press Windows logo key + P and select Extend.
- Open Settings → System → Display and use Detect to search for additional displays.
- If a display appears as “Disconnected” or similar, set it to Extend desktop to this display.
- Check multi‑monitor capability and hardware limits
- If only one external monitor works, the graphics adapter may not support more than two displays (laptop screen + 2 externals). For more than one external monitor, a docking station or USB‑C video adapter may be required.
- Avoid using a simple “display splitter” if trying to extend to more than one external monitor; those typically only duplicate the same signal, not create an extra independent display.
- Reset graphics and force detection
- Press Windows logo key + Ctrl + Shift + B to reset the graphics driver and force Windows to re-detect displays.
- If the 3rd screen still doesn’t appear, restart the PC.
- Update or roll back display drivers after the update
- In the search box on the taskbar, type device manager and open Device Manager.
- Expand Display adapters, right‑click the display adapter, select Properties → Driver.
- If the issue started right after an update and Roll Back Driver is available, select it.
- If Roll Back Driver is not available or doesn’t help, reinstall the driver:
- In Device Manager, right‑click the display adapter → Uninstall device.
- Check Attempt to remove the driver for this device and select Uninstall.
- Restart the PC if prompted.
- Open Device Manager again, right‑click the display adapter → Update driver → Search automatically for updated driver software.
- Run Windows Update again
- After a major Windows update, some device drivers may not migrate correctly. Run Settings → Windows Update and install all available updates so Windows can reinstall any missing or updated display drivers.
If the 3rd screen still isn’t detected after these steps, contact the PC or graphics adapter manufacturer to confirm the maximum number of supported displays and obtain the latest OEM graphics drivers.
References:
- Troubleshoot external monitor connections in Windows
- Roll back your display driver
- Devices not working after a major Windows update
- Docking station external monitors not working when a Windows 10 version 1703-based portable computer is connected
- how to update display drivers - Microsoft Q&A
- how to detect second monitor? - Microsoft Q&A
- How to fix compatibily between additional screen, plugged by Type "C" port" after Windows and HP update on Feb, 05th. - Microsoft Q&A
- Windows forces my monitor to "Disconnect this display" in the settings. - Microsoft Q&A