You have a power button on your monitor or your screen and if you press it only the screen goes black.
Press the no-show button of just freeze it to a black screen.
Ensure there is Power to the Monitor.
If its the monitor you are talking about then just press the "auto adjust" button, on the side of the monitor.
Push reset button.
Hold the lock button and the home button down until the screen goes black and your device should hopefully reboot.
Try another monitor on the computer and if it works correctly then the monitor is defective. Buy a new one, as it will cost more to repair than to replace.
black batton
There should be a button on-screen that can let you crouch
A screen/monitor that only shows one color except for black. Like a black and white TV or a green and black cell-phone screen.
There is no radiation from an LCD flat screen monitor. What could be dangerous is if any liquid leaks from the screen. The liquid crystals are somewhat poisonous.
Hold down the power and home button until you see an apple on the screen.