Dell P2312H Monitor - Manual (Page 39)

If either VGA or DVI-D input is selected and both VGA and DVI-D cables are not connected, a floating dialog box as shown below appears.
When the monitor enters the Power Save mode, the following message appears:
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 input