What do I do if my computer can't detect a second monitor?

The problem is likely either due to software (i.e. the app you're using or display drivers), or there's an issue with the physical connection. Make sure the second monitor is plugged in and turned on, then restart the computer. If it still won't work, make sure the correct input is selected and being used to connect to the computer. Try unplugging the cable connecting the monitor to your computer at both ends, leave it disconnected for a few minutes, then plug everything back in. If the monitor (or your computer) has multiple ports, try connecting the cable to a different one.

How do I keep my monitors from mirroring each other?

If you're using two monitors but seeing the same thing on each of them, you'll need to adjust your display settings. Press the Windows button + P to pull up the menu, then set it to Extend so that each monitor accounts for half of a shared work space. Then you can reposition the apps you want to use between each of the monitors to your liking.

Why won't my mouse move to my second monitor?

Your monitor orientation may not be set up properly. Open System Preferences and select Display > Arrangement , making sure that Mirror Displays is turned off. Before finishing, drag the screens around in the menu to make sure the settings match their orientation in your work space.

How to Fix It When a Second Monitor Is Not Working

This article describes how to troubleshoot common second-monitor problems such as no content or a black screen, an incorrect resolution, artifacts are not seen on the primary monitor, or a corrupted display. The troubleshooting steps for most of these problems are essentially the same.

Causes of Second-Monitor Problems

Secondary-display problems usually come down to a few basic causes:

The computer can't support the display in color depth, pixel count, or interface options.
The monitor's cable is damaged or malfunctioning.
The computer's display drivers aren't handling the secondary display properly.

How to Fix Second-Monitor Problems on Windows and macOS

Follow the steps below to diagnose and fix the cause of these malfunctions.

Restart the computer. This is a classic troubleshooting step because it often works. It closes other processes that might be interfering with your monitor's performance and gives you a clean slate from which to proceed.
Change the screen resolution. If the second monitor's display is blurry, pixelated, distorted, or discolored—or if it's duplicating the primary display—check the computer's display settings. If the frame rate or resolution is incorrect, adjust it there.
Adjust the scaling settings. If the windows display in different sizes on different monitors in Windows 10, adjust the scaling settings. The recommended setting will match the apparent window size across monitors as closely as possible.

In macOS, navigate to System Preferences > Displays. Select Default for display, or press Scaled and choose the correct resolution.

How to Fix Overscan in Windows 10 to Fit to Screen
Fix discoloration and color accuracy. (On macOS, use display calibration.) If the computer's settings don't fix the problem, use a hardware calibration device, or adjust the monitor's color settings, gamma, and brightness settings in the monitor's on-screen menu. Every monitor is different, but Color or Display Depth are the typical terms.

Other causes of color issues include different display panels, backlights, technologies, and age. If you need an exact match, consider professional-grade photo-editing monitors.
Adjust the monitor's refresh rate. Monitors are built to work at particular refresh rates. If your computer doesn't send a signal at one of those supported rates, there's a chance the monitor won't display the signal.

In macOS, navigate to System Preferences > Displays, and adjust the Refresh Rate drop-down menu.
Swap out the current cable. A bad cable is the most common culprit when the monitor shows artifacts or no picture at all. Very long and poorly shielded cables are especially prone to interference.

Good cables don't need to cost a fortune. Gold-plated connectors and oxygen-free copper don't provide any noticeable differences in image quality. However, poorly constructed cables can lead to issues. Purchase a cable from a trusted manufacturer. Monoprice offers an excellent combination of affordability and reliable quality.
Try the cable in alternate ports on the PC, the display, or both. Change only one at a time, so you can pinpoint which ports caused the problem. If your PC doesn't have a second compatible port, connect the monitor to a different computer to see if it works and to help pinpoint the problem.
Make sure the cable supports the correct version of the display standard. HDMI cables can support anything from HDMI 1.0, which provides minimal support, to HDMI 2.1, which can support the highest resolutions, color spaces, and audio channels.

USB-C and Thunderbolt monitors are even more confusing because the cables are physically interchangeable but not cross-compatible. DVI, meanwhile, has multiple versions, and it's possible to plug an incompatible DVI cable into a computer or monitor.

Check the cable's documentation on the manufacturer's website to find the latest display connection version supported by the cable. If the cable doesn't support your display, replace it with a cable that does. Additionally, check the appearance of the connectors on the cable, computer, and monitors to ensure they're compatible.
Remove any switches or converters from the signal chain. If the cable has HDMI on one end and DVI on the other, try a cable that has the same connector on both ends. If possible, remove or replace dongles and switches temporarily. If the simpler connection works, the removed device is to blame.

Be sure to remove one device at a time for proper troubleshooting.
Try a different display interface. For example, if the second monitor is currently connected over HDMI, use Display Port instead. This can accomplish a few things. If the current interface can't drive all the pixels in the second monitor, switching to a different interface can fix that problem.

Based on capability, common display connectors can be ranked in this order: DisplayPort, HDMI, DVI, Thunderbolt, USB-C, VGA. Unless you must use a VGA connection for legacy compatibility, avoid it; it cannot properly drive modern displays. Also, there are multiple versions of HDMI, DVI, and USB-C. Just because you can plug a cable into a port doesn't mean you'll have full compatibility.
Update the computer's display drivers. If you have a third-party discrete graphics card, update the drivers from the manufacturer. If you plug the monitor into the motherboard's display connectors, visit the motherboard or computer manufacturer's website to check for updated drivers for those features.
Lower the image quality. If the monitor suffers from a poor frame rate, choppiness, or corrupted video or game content, reducing the signal's complexity can help. For games, try the lowest-quality settings first, then gradually improve the quality until the issue reappears. For video content, try a lower resolution or a less demanding frame rate.
Check the power connections. If the monitor doesn't turn on, try different power connectors or wall outlets. Test wall outlets with other devices before plugging in the monitor to ensure those devices work properly.
Check the monitor's input settings. If the monitor has multiple input interfaces, make sure you have the correct one selected in the monitor's on-screen menu. Most monitors have an auto-detect feature that automatically switches to the connector receiving the signal. When that doesn't work, set the display connector manually.
Make sure the monitor can display the content sent to it. Does the monitor have sufficient color gamut, resolution, or bit depth to display the content properly? Consult the monitor's documentation or the monitor manufacturer's website.
If none of these steps fix the problem, you might need to replace the monitor. If you see colored lines, black or colored points, or cracks in the image, the monitor's panel might be damaged and require replacement. These display issues can be fixed similarly on macOS.

FAQ

What do I do if my computer can't detect a second monitor?

The problem is likely either due to software (i.e. the app you're using or display drivers), or there's an issue with the physical connection. Make sure the second monitor is plugged in and turned on, then restart the computer. If it still won't work, make sure the correct input is selected and being used to connect to the computer. Try unplugging the cable connecting the monitor to your computer at both ends, leave it disconnected for a few minutes, then plug everything back in. If the monitor (or your computer) has multiple ports, try connecting the cable to a different one.
How do I keep my monitors from mirroring each other?

If you're using two monitors but seeing the same thing on each of them, you'll need to adjust your display settings. Press the Windows button + P to pull up the menu, then set it to Extend so that each monitor accounts for half of a shared work space. Then you can reposition the apps you want to use between each of the monitors to your liking.
Why won't my mouse move to my second monitor?

Your monitor orientation may not be set up properly. Open System Preferences and select Display > Arrangement, making sure that Mirror Displays is turned off. Before finishing, drag the screens around in the menu to make sure the settings match their orientation in your work space.

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