My Windows Monitors stopped extending from the main screen to the #2. Even with new hdMi cord

1. Press Windows logo key + P and make sure Extend is selected. If it is already selected, switch to another mode and then back to Extend.
2. Disconnect anything extra from the PC, including docks, dongles, and adapters. These can cause display conflicts.
3. Check the monitor connection again:
   • Make sure the HDMI cable is firmly connected on both ends.
   • Since a new cable was already tried, test the monitor with a different system if possible to confirm the monitor is still receiving video correctly.
4. If the PC has more than one video output port, connect the monitor to a different video output port.
5. Reset the graphics driver:
   • Press Windows logo key + Ctrl + Shift + B.
   • If that does not help, restart the PC from Start > Power > Restart.
6. If the problem started after an update, roll back the display driver:
   • In the taskbar search box, type Device Manager.
   • Open Device Manager and expand Display adapters.
   • Right-click the display adapter, select Properties > Driver tab > Roll Back Driver.
   • If Roll Back Driver is unavailable, continue with reinstalling the driver.
7. Reinstall the display driver. This can temporarily affect display output while Windows reinstalls it:
   • Open Device Manager.
   • Expand Display adapters.
   • Right-click the display adapter and select Uninstall device.
   • Select Attempt to remove the driver for this device, then select Uninstall.
   • Restart if prompted.
   • Open Device Manager again.
   • Expand Display adapters.
   • Right-click the display adapter and select Update driver.
   • Select Search automatically for updated driver software and complete the installation.
8. If one external monitor works but adding another does not, the graphics adapter may not support more than one external monitor. Also, a display splitter cannot extend to multiple monitors because it duplicates the same signal.
9. If the issue continues after these steps, file a report in Feedback Hub with the monitor setup details and the steps that reproduce the problem.

References:

• Troubleshoot external monitor connections in Windows
• Display configuration reverts to "Second screen only" after you resume from standby
• Troubleshooting blank screens in Windows