Symptoms
- Monitor stays black or says 'no signal'
- Monitor works when connected via HDMI but not USB-C
- Monitor flickers on then off
- Monitor detected but shows wrong resolution or refresh rate
Likely causes
- CommonUSB-C cable or port doesn't support video (Alt Mode)Not all USB-C cables and ports carry a video signal; some are data or charge only.
- CommonMonitor set to the wrong input sourceMonitors need the correct input selected on their own on-screen menu.
- PossibleLaptop's graphics driver needs updatingOutdated graphics drivers can fail to detect or properly output to external displays.
- PossibleCable or port not seated firmlyUSB-C connectors can appear seated but not click fully into place.
- Less commonMonitor or dock hardware faultA failing dock or monitor input can prevent detection even with the correct cable.
What to do
- Confirm the monitor's input source is set to the correct USB-C/DisplayPort input on its menu.
- Try a different USB-C cable that's rated for video (often labeled 'DisplayPort Alt Mode' or 'Thunderbolt').
- Try a different USB-C port on the laptop, since not all ports support video output.
- Press Windows key + P (or use display settings) to check if the system detects an external display even without image.
- Update the laptop's graphics driver from the manufacturer's website.
- Test the monitor with an HDMI cable if available to confirm the monitor itself works.
- Restart both the laptop and the monitor with the cable connected.
Tools and parts
- None
USB-C to USB-C video cableSearch: “USB-C DisplayPort alt mode cable”
When to call a pro
If a known-good cable and port still won't detect the monitor while HDMI works fine, the laptop's USB-C video output may be a hardware fault worth a professional check.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.