ScreensieHardware
How to Detect a Second Monitor
Make Windows search for a connected display.
Follow the steps in order and stop if the screen or target does not match what is described. Use administrator access only when the task requires it.
Check power and cable
Turn on the monitor, select the correct input, and reseat the cable at both ends.
Open Display settings
Right-click the desktop and select Display settings.
Detect the display
Expand Multiple displays and select Detect.
Choose a layout
If detected, select Extend these displays, then arrange the numbered rectangles to match the desk.
If it remains missing
Try another known-good cable or port and check Device Manager before installing any driver.