http://support.dell.com/support/edocs/MONITORS/U2711b/en/ug/solve.htm#Common Problems
Self-Test
Your monitor provides a self-test feature that allows you to check whether your monitor is functioning properly. If your monitor and computer are properly connected but the monitor screen remains dark, run the monitor self-test by performing the following steps:
Turn off both your computer and the monitor.
Unplug the video cable from the back of the computer. To ensure proper Self-Test operation, remove both Digital (white connector) and the Analog (blue connector) cables from the back of computer.
Turn on the monitor.
The floating dialog box should appear on-screen (against a black background) if the monitor cannot sense a video signal and is working correctly. While in self-test mode, the power LED remains blue. Also, depending upon the selected input, one of the dialogs shown below will continuously scroll through the screen.......................
or
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:
Ensure that the screen is clean (no dust particles on the surface of the screen).
Unplug the video cable(s) from the back of the computer or monitor. The monitor then goes into the self-test mode.
On the front panel, touch and hold the button 1 and button 4 keys on the front panel, simultaneously for 2 seconds. A gray screen appears...............................................................