Symptoms
- Only one monitor shows a picture even though two are connected
- Windows Display settings show only one monitor, or shows a second as 'not connected'
- Second monitor works fine when swapped to the first monitor's cable/port
- Problem started after a driver update or new cable
Likely causes
- CommonCable not fully seated at either the monitor or the GPUA loose HDMI or DisplayPort connection is the most frequent cause.
- CommonMonitor set to the wrong input sourceEspecially likely if the monitor has multiple inputs and none is auto-detecting.
- PossibleGPU output port limitation or needing a specific combination of ports for multiple displaysSome GPUs have restrictions on which port combinations support multiple monitors at once.
- PossibleGraphics driver not properly detecting the second displayA driver update or reinstall often resolves detection issues.
- PossibleFaulty cable or the second monitor's input portTesting with a different cable rules this in or out.
What to do
- Confirm the second monitor's cable is fully seated at both ends.
- Check the monitor's input source setting matches the port being used.
- In Windows, go to Display settings and click 'Detect' to force a re-scan for connected displays.
- Try swapping which monitor uses which cable and port to see if the problem follows the monitor or the port.
- Update the graphics driver to the latest version from the manufacturer's website.
- Check the GPU's manual for any limitations on which combination of ports supports multiple simultaneous displays.
Tools and parts
- Spare HDMI/DisplayPort cable
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.