Dell P1913 - Page 45

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 1440 x 900 (for the P1913)/1280 x 1024 (for the P1913S)/1680 x 1050 (for the P2213).
You will see the following message before the DDC/CI function is disabled:
When the monitor enters the Power Save mode, the following message appears: