Check that the cables are connected to the right ports on the monitor and room device or laptop.

Check that you have selected the correct input on your monitor.

Swap the suspected cable to another standard cable. Use one that is within the specifications for the cable type. If you are running cables at the limits of length specifications, try a cable that is well within the specifications and has no extenders, splitters, or converters attached. Then restart all equipment.

Check that the cable works with other equipment.

Confirm that another device connected to same input on the screen is displayed correctly.

If possible, connect the video system or laptop to another monitor to check whether the issue is with the monitor.