Second Monitor Not Detected
A second monitor, connected via HDMI, DisplayPort or USB-C, either isn't detected by Windows, shows a blank screen, or doesn't extend the desktop properly.
Quick answer: Most second-monitor problems come down to the cable or port rather than the monitor or computer being faulty — try a different cable and a different port before changing any settings. If the monitor is detected but not displaying correctly, Windows' Display settings usually resolves it in a couple of clicks.
Likely causes
- A faulty or loose cable, or a cable plugged into the wrong port on a computer with multiple graphics outputs
- The monitor set to the wrong input source
- Windows Display settings set to duplicate rather than extend, or not detecting the second screen automatically
- A graphics driver that needs updating
What you can safely check yourself
- Right-click the desktop, choose Display Settings, and click "Detect" to force Windows to look for the second monitor
- Try a different cable and port
- Check the monitor itself is on the correct input source
- If the computer has both onboard and dedicated graphics, make sure both monitors are plugged into the same one
When it needs a proper look
If Detect doesn't find it, a known-working cable and port don't help, and the monitor works fine on another computer, the fault is likely the graphics output on your computer and worth a proper look.