Dell C8618QT User Manual page 49

If you press any button other than the power button, the following messages will appear
depending on the selected input:
If either HDMI 1, HDMI 2, HDMI 3, HDMI 4, DP or VGA input is selected and the corresponding
cable is not connected, a floating dialog box as shown below appears.
or
or
Operating the Display | 49