Why my labtop turn on indication show but display fully blank.

@karthick20070 we need to know the exact model for your laptop. The very first thing you want to do is to check if this is possibly a bad backlight. A simple check for that would be to darken the room and turn the computer on. Then use a flashlight and angle the light at the screen on different areas. You might make out some shadows or see a slight grey color. If co it's your backlight. that can be your backlight array or the backlight circuitry on your motherboard. Next connect an external monitor to your laptop. If that displays your desktop properly, you know that you have an issue with other your LCD screen or with the video circuitry on your motherboard. Let us know what you find out.