TV starts after repeatedly switching on & off

Try unplugging the TV for 20-30 seconds to reset the control panel.

@prashantde30600 you did not tell us what it exactly is the TV is doing. We will need to know how it switches off and on and if the power LED turns on and off or if it just the picture that turns off and on. There are two distinct possibilities. One it's a bad power supply, the other is a bad backlight especially the "Sometimes starts but no display, only sound" would lead me to the backlight. Next time it does turn on and you do have sound, darken the room and use a flashlight and shine the beam at an angle against the screen. If you can make out shadows or shapes, then it is your backlight that has failed.

Remove the back cover from your TV after you unplug it. Then visually inspect all of the boars for any damaged looking component, lose ribbon cable etc. Take some well focused pictures of each board and post those with your Question. That way we can see what you see and hopefully we can help you to fix your TV. Adding images to an existing question