Dell P1913 Monitor - Manual (Page 46)

Activate the computer and wake up the monitor to gain access to the OSD .
If you press any button other than the power button, one of the following messages will appear depending on the selected input:
VGA/DVI-D/DP input
If either VGA or DVI-D or DP input is selected and the corresponding cable is not connected, a floating dialog box as shown below appears.
or or
See Solving Problems for more information.