@Vasanth31
It could be any and all of the following issues:
1) cable fault
2) video chip fault
3) Screen fault
To check 1), you would have to use a different video cable.
To check 2) and 3), you would have to connect a different screen -- after confirming the cable was not the issue. If the issue appears on the new screen, it is a video chip fault; if not, it is a screen fault -- and you would have to replace the monitor.
I am a volunteer and I do not work for, nor represent, HP