Dell U3014 Monitor - Manual (Page 64)

or
4. This box also appears during normal system operation if the video cable becomes disconnected or damaged.
5. Turn Off your monitor and reconnect the video cable; then turn On both your computer and the monitor.
If your monitor screen remains blank after you use the previous procedure, check your video controller and computer, because your monitor is functioning properly.
Built-in Diagnostics
Your monitor has a built-in diagnostic tool that helps you determine if the screen abnormality you are experiencing is an inherent problem with your monitor, or with your computer and video
card.
NOTE: You can run the built-in diagnostics only when the video cable is unplugged and the monitor is in self-test mode.
To run the built-in diagnostics:
1. Ensure that the screen is clean (no dust particles on the surface of the screen).
2. Unplug the video cable(s) from the back of the computer or monitor. The monitor then goes into the self-test mode.