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Monitor Connection Check

Find the next useful test for a missing, black or intermittently disconnected monitor. Run this check on the affected computer.

Processed on your deviceFree · No account needed

Preparing your tool…

How to use it

  1. Open this tool on the affected computer. Choose what is happening, or choose the general screen check.
  2. Follow the short instructions and say whether they helped. Confirm the result only when all intended screens show the picture you want.
  3. If useful, open More checks & technical details for optional display detection, cable comparisons and observation. Save your work before disconnecting a dock or cable.
  4. Review the report, remove any details you do not want to share, then copy, download or print it yourself.

You expect two external displays. The browser reports two, but one stays black. The visible result remains unresolved; next check that monitor’s power, brightness and selected input.

Details & limits

Run on the affected computer. Automatic display information depends on browser support and permission; a manual check remains available. Browser reports do not prove a visible picture, cable condition or a repaired connection.

Does a missing display prove that its USB-C cable is broken?

No. Browser access, system display settings, mirroring, ports, a dock or the monitor input can affect the result. A working HDMI connection from another computer does not test this USB-C path. Compare one controlled change at a time and keep browser reports separate from your observations.

A second monitor is missing or stays black: what can a browser check?

With your permission, a supporting browser reports the displays available to it and changes during an active observation. You confirm whether each monitor actually shows a picture. Mirrored, disabled or virtual displays can make this report differ from the physical desk. A reported display can still be black, and a missing display does not prove a broken cable. The guided check separates browser information, your observations, possible explanations and facts it cannot determine. You can follow the manual steps without automatic detection.

Related tools

Monitor & Touch TestMeeting Device Check
Help with USB-C interruptions and verified sources

USB-C fails while HDMI works

A picture over HDMI from a second computer confirms that source and connection path. It does not test the other computer’s USB-C cable or monitor input. Select the intended input on the monitor. Then change just one cable or port and record the visible result. If both monitors work separately but not together, the shared connection path and supported display configuration remain open questions.

Save your work before reconnecting anything. A USB-C connection or dock may also carry storage and other devices. On a work computer, put driver, firmware and model questions in the report for your IT team.

Display settings for your operating system

Windows: open Settings → System → Display → Multiple displays → Detect. For separate workspaces, press Windows + P and choose Extend. On macOS, open the Apple menu → System Settings → Displays. Hold Option and choose Detect Displays when the button appears. Afterwards, check for a visible picture yourself.

Connection check or pixel inspection?

This connection check helps compare missing displays, black screens and reported changes. The separate Monitor Test provides calm color patterns and touch paths for visual inspection. Neither tool repairs cables or pixels or reliably measures native panel resolution or cable quality.

Technical sources and manufacturer help

Documentation checked on 26 September 2026; this is not a hardware test.