Follow these troubleshooting steps to identify and fix the issue:
Check the cable connection between the laptop and external monitor, make sure it is correctly and firmly plugged in.
If your cable is connected, try another cable. Make sure its compatible with both your laptop and external monitor.
Check if your external monitor is properly powered on and active.
Ensure that the resolution for both the external monitor and laptop's graphic card are set to the same resolution.
Restart your laptop and external monitor making sure that both have fully restarted.
Test the issue on an alternate display.
