Symptoms
- Only one monitor lights up or shows an image
- Second monitor shows 'no signal'
- Monitors were both working, now one dropped
- Desktop only extends to one screen even though both are connected
Likely causes
- CommonCable not fully connected or faultyA loose HDMI/DisplayPort cable is the most common reason a second monitor drops out.
- CommonGraphics card doesn't have enough active outputs enabledSome graphics cards or laptops need the display mode manually set to extend rather than duplicate.
- CommonMonitor set to wrong input sourceThe monitor may be powered on but looking at an input with nothing connected.
- PossibleOutdated graphics driverDriver bugs can cause a monitor to be detected inconsistently.
- Less commonFaulty monitor or cable portA damaged port on the monitor or graphics card can prevent a stable connection.
What to do
- Check that the cable is fully seated at both the monitor and computer ends, and try a different cable if available.
- On the monitor, press its input/source button and confirm it's set to the port you're using.
- Right-click the desktop, choose Display settings, click Detect, and make sure 'Extend these displays' is selected.
- Try connecting the second monitor to a different port on the computer (or graphics card if there are several).
- Update the graphics driver from the manufacturer's website (NVIDIA, AMD, or Intel).
- Restart the computer with both monitors connected and powered on.
- Test the second monitor with a different cable and computer to confirm the monitor itself works.
Tools and parts
- None
Replacement video cableSearch: “HDMI or DisplayPort cable”
When to call a pro
If a monitor won't be detected on any port or computer with a known-good cable, the monitor's input board may have failed and needs professional repair or replacement.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.