Computers · Repair guide

How to fix a second monitor not detected

10 fixes, easiest first4 min readUpdated November 2026

Quick fix

Check that both ends of the cable are firmly plugged in and the monitor's input is set to the port you're using, then press Windows + P and choose Extend. If it still doesn't appear, go to Settings > System > Display > Multiple displays and select Detect.

What it means

When a second monitor stays black, says "No signal" or doesn't appear in Windows display settings, the computer isn't receiving or sending a picture to it. The usual causes are a loose or faulty cable, the monitor set to the wrong input, Windows set to show only one screen, a dock or adapter that doesn't support video, or a graphics driver problem.

Common causes

  • A loose, faulty or unsuitable cable
  • The monitor is set to the wrong input (for example HDMI 2 instead of HDMI 1)
  • Windows is set to show the picture on only one screen
  • A dock, hub or adapter that doesn't support video, or is faulty
  • A graphics driver problem, often after an update
  • The computer or graphics card can't run that many monitors

How to fix it

Work down the list. Each fix is safe to try before moving on to the next.

01Check power, cable and inputEasy

  1. Make sure the monitor is plugged in and turned on; its power light should be lit.
  2. Firmly push in the video cable at both ends.
  3. Use the monitor's own buttons to open its menu or input button and choose the port you're using, such as HDMI 1, HDMI 2 or DisplayPort.
  4. "No signal" on the monitor means it is on but not getting a picture from that input, so the cable, port or input setting is the usual cause.

Why it helps: Most "no signal" cases come down to a loose cable or the monitor watching the wrong input.

02Press Windows + P and choose ExtendEasy

  1. Press Windows + P on the keyboard.
  2. Select Extend to use the second monitor as extra space, or Duplicate to show the same picture on both.
  3. If PC screen only was selected, Windows was deliberately ignoring the second monitor.

Why it helps: Windows may be set to show the picture on only one screen.

03Make Windows detect the monitorEasy

  1. Open Settings > System > Display.
  2. Select Multiple displays to expand it, then select Detect.
  3. If two screens now appear, select Identify to see which number belongs to which monitor.
  4. Drag the screen boxes to match how the monitors sit on your desk, then select Apply if asked.

Why it helps: Detect makes Windows look again for a monitor that was connected after the PC started.

04Try another cable, port and remove adaptersEasy

  1. Unplug any docks, hubs, dongles or adapters and connect the monitor straight to the computer if you can.
  2. Try a different cable. If the new one works, the old one was faulty.
  3. Try another video port on the computer (HDMI, DisplayPort, USB-C) if it has one.
  4. On a laptop, a USB-C port only carries video if it supports it (DisplayPort Alt Mode or Thunderbolt); check your laptop's specifications.
  5. Test the monitor with another computer to find out whether the monitor or the PC is the problem.

Why it helps: Cables, adapters and docks fail often, and not every port can carry a video signal.

05Reset the graphics driver and restartEasy

  1. Press Windows + Ctrl + Shift + B. The screen may flash or beep briefly while the graphics driver restarts.
  2. If that doesn't help, select Start > Power > Restart.
  3. If it still fails, select Start > Power > Shut down, wait, and turn the PC back on with the monitor already connected.

Why it helps: A quick driver reset or full restart often brings back a monitor that used to work.

06Install Windows and driver updatesEasy

  1. Open Settings > Windows Update and select Check for updates; install everything and restart.
  2. Go to Settings > Windows Update > Advanced options > Optional updates and install any display driver updates listed.
  3. You can also get the latest graphics driver from your PC maker's website or the graphics card maker's website.
  4. If you use a dock, check its maker's website for firmware or driver updates.

Why it helps: Updated graphics and dock drivers fix many detection problems.

07If you're adding a third monitor, check the limitsEasy

  1. Get one external monitor working on its own first.
  2. Check with your PC or graphics card maker how many monitors it supports at once.
  3. A display splitter only copies one picture to several screens; it can't extend your desktop across them.
  4. If you're out of video ports, a docking station recommended by your PC maker, or a USB-C video adapter, can add more.

Why it helps: Every computer has a maximum number of screens it can drive, and splitters only duplicate.

08If you use a Mac, detect the display manuallyEasy

  1. Unplug the display from the Mac and from power, then plug both back in. Connect it directly, not through a hub or dock.
  2. Put the Mac to sleep and wake it; on a MacBook you can close the lid for a few seconds and open it again.
  3. Open Apple menu > System Settings > Displays, press and hold the Option key, and click Detect Displays when it appears.
  4. If the Mac asks whether to allow the accessory to connect, choose to allow it.
  5. Check Apple's specifications for your Mac model to see how many external displays it supports, then install macOS updates from System Settings > General > Software Update.

Why it helps: Macs may need a nudge to find a new display, and some models support only one external screen.

09If it stopped after a driver update, roll back the display driverMedium

  1. Right-click Start and select Device Manager.
  2. Expand Display adapters.
  3. Right-click your graphics adapter, select Properties, open the Driver tab and select Roll Back Driver.
  4. Pick a reason, confirm, and restart the PC.
  5. If Roll Back Driver is greyed out, there is no older driver saved; use the next fix instead.

Why it helps: A new graphics driver can break support for an extra monitor; going back to the previous one restores it.

10Reinstall the display driverAdvanced

  1. Warning: while the driver is removed, your screen may go blank for a moment and look low resolution until it is reinstalled. Save your work and write these steps down first.
  2. Open Device Manager and expand Display adapters.
  3. Right-click your graphics adapter and select Uninstall device.
  4. Tick the option to attempt to remove the driver, then select Uninstall, and restart if asked.
  5. Open Device Manager again, right-click the adapter under Display adapters, select Update driver, then Search automatically for drivers.
  6. If Windows can't find one, install the driver from your PC maker or graphics card maker.

Why it helps: A fresh driver install fixes damaged driver files that a rollback or update can't.

Check it's fixed

  • The second monitor shows your desktop instead of "No signal".
  • Two screens appear in Settings > System > Display, and Identify shows a number on each.
  • The monitor still works after a restart and after waking the PC from sleep.

When to get help

If the monitor shows "No signal" on every computer and cable you try, the monitor is likely faulty; contact its maker. If no external monitor works on any port of your PC, contact the PC maker or a repair shop.

Questions

Why does my monitor say no signal on HDMI?

The monitor is on but isn't receiving a picture from the input it's set to. Check the cable at both ends, choose the right HDMI input with the monitor's buttons, and press Windows + P to pick Extend.

Why did my second monitor stop working after a Windows update?

The update may have changed the graphics driver. Press Windows + Ctrl + Shift + B, check for newer updates, and roll back the display driver in Device Manager if needed.

Can I use an HDMI splitter for dual monitors?

A splitter only shows the same picture on both screens. To extend your desktop you need a second video port, a suitable dock or a USB-C video adapter.

Why won't my MacBook show on two external monitors?

Some Mac models support only one external display. Check Apple's specifications for your model to see how many it supports.

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