Greetings SHIRIKANT,
If you could, please provide us with more information about the issue you are having with the display.
For example, if there is no information displayed on the LCD screen when shooting, then let's press the INFO button to toggle the display back on and cycle through the different views until you reach the one you were used to seeing.
If you are wanting to shoot through the LCD screen instead of the viewfinder on the EOS 5D Mark III camera, then let's press the START/STOP button while the camera is in the picture taking mode to enable the Live View shooting function.
If you are wanting to view what you're shooting in the video shooting mode on an external display, then let's ensure that the HDMI cable is properly connected to the camera as well as the external display. You may also test to see if a different HDMI cable will resolve the issue.
