Check the monitor is on the right input (HDMI/DisplayPort), reseat or swap the cable, press Win+P and choose Extend, then Settings → System → Display → Multiple displays → Detect. Update or reinstall the graphics driver if it still isn't found.

The short explanation

Detection happens at several layers: the cable and port, the monitor’s input, any dock or adapter in between, the graphics driver, and Windows’ display mode. A fault at any layer gives the same result.

USB-C and Thunderbolt docks add another variable: the laptop’s port must support video output (DisplayPort Alt Mode or Thunderbolt), and docks often need firmware and driver updates.

What you'll see

  • Second monitor shows “No signal”.
  • Display settings show only one screen.
  • Monitor detected but mirrored instead of extended, or wrong resolution.

What causes it

  • Loose/faulty cable or wrong monitor input.
  • Projection mode set to PC screen only or Duplicate.
  • Dock, adapter or USB-C port without video support.
  • Outdated or corrupted graphics driver.

How to fix it

  1. Check cable and inputReseat both ends, try another cable and port, and use the monitor's menu to select the correct input.
  2. Set projection modePress Win+P and choose Extend.
  3. Detect displaysSettings → System → Display → Multiple displays → Detect.
  4. Restart the graphics driverPress Win+Ctrl+Shift+B. The screen flickers as the driver reloads.
  5. Update the graphics driverInstall the latest driver from Intel, AMD or NVIDIA (or the laptop maker). Reinstall it if updating doesn't help.
  6. Check docks and adaptersConnect the monitor directly to the PC to test. Update dock firmware/drivers (e.g. DisplayLink) if the dock is involved.
How to tell it worked: Display settings show both screens and you can drag windows between them.

Stop it happening again

Use certified cables and docks matched to your laptop's ports, and keep graphics drivers current.