Your computer or notebook screen is black, unresponsive midnight black. Most often, it is not a serious problem and the fix is easy. Occasionally, you will need to call a technician for help.
In an attempt to save power, especially for notebooks on a battery, computers will enter sleep mode and shut down the monitor. One of the following methods will wake your computer: clicking a mouse button, moving the mouse, pressing the spacebar or pressing the power button. Your monitor will turn back on when the computer wakes. Changing the power option (found in the Control Panel) to never turning off the monitor will prevent this from recurring.
One of the options for screensavers is to simply shut off the monitor or go "blank." Password-protected screensavers may also go blank. If you find your computer monitor turning black after a few minutes of inactivity, check your screensaver settings.
Sometimes the wires within the hinges of a notebook cover can break, causing the screen to stay black no matter what you press. To test for this problem, try attaching an external monitor to the notebook (refer to your owner's manual for how to do this). If the external monitor works, call your notebook dealer for repair options.
Are the cables behind your computer sitting on the floor? Has your coworker run over them with his wheeled chair? If the monitor on a desktop computer stays black, it is possible that the power cable has been broken. Try a different power cord and see if the screen turns on.