@ssm73 you are saying that the power stays on. Let us know about the sound (if it stays on) as well. It is possible that this is a bad backlight that just turns your screen off and on. It is somewhat important that we know what you tried to fix this. We don't have to go through things you already did, so let us know what you've tried.
First you need to rule out your inputs as error source. Remove all of them (especially if you have some sort of cable box, sat box etc.). Unplug your TV and unplug all input sources. Hold down the power button for 30-60 sec. Then reconnect one input source (preferably local, something like Game console, DVD/BR player). and make sure you use a known-well HDMI cable, if that's how you connect. Lastly reconnect the TV and try to turn it on. See if that changes anything.
After that you want to remove the back cover from your TV and take a look at the boards. Check for anything odd, like missing or burned looking components. Post some good pictures of all the boards and cables with your QUESTION. That way we can see what you see.
Adding images to an existing question - iFixit Repair Guide
Check the power board and see if the cable that goes to the backlight is properly seated and if there are components around it that look "odd" (failed Diodes are common). You can also measure the voltage on those connectors to make sure that you a. have the proper voltage and b. keeps the power on. You will have a voltage drop as the light turn off, but it should be within "reason".
Thank you very much . I have done majority of what you said removed every box from tv. I had tv completely unplugged and just plugged in to socket. However soon I turn on same thing happened like it’s gone in to same position where it was 15min ago although was switched off for 15min. Will try tomorrow to add some pictures . I would describe this like tv being in the standby like position . On a moment when I turn volume I would get some sound for like a second without picture but apart of that is just black screen going to but of lighter screen and so on . Definitely will post more info tomorrow. Many thanks for your help