Second Monitor Not Detected

A second monitor not detected means Windows or macOS does not know the screen is there: Display settings shows one screen, and the other stays black or says no signal. The usual causes are the monitor set to the wrong input, a cable or adapter that does not carry video, Windows set to show the picture on one screen only, or a graphics driver that needs a reset. The quickest fixes are to choose the right input in the monitor's own menu, press Windows + P and choose Extend, then select Detect in Display settings. Once both screens show, the screen resolution test confirms each one runs at its real resolution and the refresh rate test confirms its refresh rate.

Quick checks

• Power and input. Check the monitor's power light, then open its menu and pick the input you plugged into, such as HDMI 1, HDMI 2, DisplayPort or USB-C. Automatic input search often stops on the wrong port.
• Display mode. Press Windows + P and choose Extend. PC screen only keeps the second monitor dark even when Windows sees it.
• Reset the graphics driver with Windows + Ctrl + Shift + B.
• Cable and port. Reseat both ends, then try another cable and another port on the computer.
• Docks and adapters. Unplug them and connect the monitor straight to the computer. Microsoft notes that docks, dongles and adapters can cause conflicts.

Use Detect in Display settings

Windows 11: open Settings, System, Display, expand Multiple displays and select Detect. If two boxes appear at the top of the page, select Identify to see which number belongs to which screen.

Windows 10: open Settings, System, Display, scroll to Multiple displays and select Detect.

If the second screen shows in Display settings but stays dark, look at the drop-down under the screen boxes. Show only on 1 turns the second screen off. Choose Extend these displays and select Keep changes.

Check the cable, port and adapter

• USB-C to a monitor works only if that USB-C port carries video. Look for a DisplayPort or Thunderbolt symbol next to it, or check the computer's specifications. A charge-only or data-only USB-C port shows nothing.
• Adapters work in one direction. A DisplayPort to HDMI adapter takes a DisplayPort output to an HDMI monitor. Going from an HDMI output to a DisplayPort monitor needs an active, powered converter.
• Splitters copy, they do not extend. A display splitter sends the same picture to both screens and Windows still sees one monitor.
• Desktops with a graphics card. Plug the monitors into the card, not the motherboard. The motherboard's ports usually switch off when a card is fitted, unless the integrated graphics are turned on in the BIOS (often called iGPU Multi-Monitor).
• How many screens your graphics support. Some graphics cards and laptops drive fewer screens than they have ports. Check the maker's specifications for the maximum number of displays.

Roll back or reinstall the graphics driver

If the second monitor disappeared after a Windows or driver update, roll the driver back:

1. Search the taskbar for Device Manager and open it.
2. Expand Display adapters, right-click your graphics adapter and select Properties.
3. On the Driver tab, select Roll Back Driver, then restart.

If there is no older driver, reinstall it: right-click the adapter, select Uninstall device, tick Attempt to remove the driver for this device, restart, then install the newest driver from NVIDIA, AMD, Intel or your laptop maker. If the adapter shows as Microsoft Basic Display Adapter, no proper graphics driver is installed at all, and multiple screens will not work properly until one is.

Not detected after a restart, sleep or power cut

• After a restart or sleep: DisplayPort monitors in particular can fall into a deep sleep and miss the computer starting up. Turn the monitor on before the computer, and switch off any deep sleep or auto power off option in the monitor's menu. If it only happens after a full shutdown, turn off Turn on fast startup in Control Panel, Power Options, Choose what the power buttons do.
• After a power cut: check that the monitor shows its own menu. Try a different input on the monitor and a different port on the computer, since a surge can damage a single port. Reset the monitor to its factory settings from its menu.

Docking stations and USB-C hubs

A dock adds another link that can fail, so test without it first.

• Connect the dock's own power adapter. Many docks will not drive screens on laptop power alone.
• DisplayLink docks need the DisplayLink driver installed on the computer, or the screens stay blank.
• Two screens on one USB-C cable rely on a feature called MST. Windows supports it. macOS does not extend screens over MST, so on a Mac, two monitors on a basic USB-C hub show the same picture.
• Update the dock's firmware from its maker, and the laptop's BIOS and graphics driver from the laptop maker.

Gaming laptops with a MUX switch or GPU modes

Many gaming laptops wire the HDMI port straight to the dedicated NVIDIA or AMD graphics, while USB-C may connect to the processor's own graphics. If the dedicated graphics are switched off to save battery, the port wired to them goes dark.

• ASUS: in Armoury Crate, under GPU Mode, Eco Mode turns the dedicated graphics off so it disappears from Device Manager. Switch to Standard and plug the monitor in again.
• Lenovo Legion, MSI and others have similar GPU modes in Lenovo Vantage, Legion Space or MSI Center. Choose a mode that keeps the dedicated graphics on.
• Changing a MUX switch or GPU mode needs a restart. If the monitor still does not appear afterwards, reinstall the graphics driver.

Second monitor not detected on a Mac

1. Open System Settings, then Displays. Hold the Option key to show Detect Displays and click it.
2. On an Apple silicon MacBook, look for a message asking you to allow the accessory to connect, and allow it.
3. Put the Mac to sleep and wake it, or close the lid for a few seconds and open it again.
4. Connect the display directly, not through a hub. A USB-C adapter must support DisplayPort Alt Mode or Thunderbolt.
5. Check how many displays your Mac supports in its tech specifications, under Display Support or Video Support. MacBook Air and 13 inch MacBook Pro models with M1 or M2 drive one external display. Base M3 models drive a second one only with the lid closed. Base M4 models and later drive two with the lid open. Beyond that, a DisplayLink dock with its driver can add more.

If the screen is detected but flickers or shows sparkles, see screen flickering. If it stays on a no signal message, the steps in hdmi no signal on monitor go further into inputs, consoles and adapters.

When it is a hardware fault

Unplug the video cable and turn the monitor on. Most monitors then show a self test box or a no signal message, which proves the monitor's electronics work. Plug the monitor into another computer, as Microsoft suggests, or plug a monitor you know works into yours, to find out which side is at fault. A monitor that works elsewhere points to the computer's port or graphics, and a port that stopped working after a power cut is a repair for the computer, not the monitor.

Within warranty, a monitor that shows no picture from any computer is a straightforward claim. Note the ports and cables you tried. Once it works, run the monitor test on the new screen to check it for dead pixels and uneven backlight while you can still return it.

Second monitor questions