Second monitor not detected by the computer

Symptoms

• Only the main monitor shows a desktop image
• Second monitor stays black or says 'No Signal'
• Display Settings shows only one monitor listed
• Second monitor worked before but stopped being detected

Likely causes

• CommonCable not fully connected or faultyBoth monitors need a firmly seated cable into a working port.
• CommonGraphics card port limitationSome GPUs can't run two monitors from certain port combinations, especially older integrated graphics.
• CommonDisplay set to 'duplicate' or the second display disabled in settingsWindows can be configured to ignore the second monitor entirely.
• PossibleOutdated graphics driverDriver bugs can prevent proper multi-monitor detection.
• PossibleSecond monitor is on the wrong input sourceEven when correctly cabled, the monitor's onscreen menu may be set to a different input.

What to do

1. Confirm the second monitor is powered on and set to the correct input source using its onscreen menu.
2. Reseat the cable at both the monitor and the computer, trying a different port on the computer if available.
3. Press the Windows key + P and choose 'Extend' or 'Duplicate' to force Windows to look for a second display; on Mac, go to System Settings > Displays and click 'Detect Displays.'
4. Open Display Settings and click 'Detect' to prompt the OS to search again for connected monitors.
5. Try a different cable and, if possible, a different type of port (for example DisplayPort instead of HDMI).
6. Update your graphics driver from the manufacturer's website and restart the computer.
7. Test the second monitor alone as the only connected display to confirm the monitor itself works.

Tools and parts

• None

When to call a pro

If the second monitor works fine when it's the only display connected but still won't show up alongside the first, the graphics card's multi-display support or a driver conflict is likely, which a computer technician can diagnose.

Safety