Dell U2713HM User Manual page 46

This means that the monitor cannot synchronize with the signal that it is receiving from the computer. See Monitor Specifications for the Horizontal and
Vertical frequency ranges addressable by this monitor. Recommended mode is 2560 x 1440.
You will see the following message before the DDC/CI function is disabled.
When monitor enters 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/DP/HDMI input