I have solved this issue. This is a motherboard problem and more specific on the baseband. This need microsoldering skills and you have to reball or replace the baseband.

Well, I swapped the screen with another laptop I had and I saw that finally @jayeff was right, LVDS cable had problem and that was the reason of the flickering screen.

Thank you for your feedback. I found the solution finally, it was bios problem.

I don’t know what the problem was, but I updated bios and then reset it to default setting and somehow it worked. Now I also overclocked ram and everything works perfectly!! Thank you very much for the respond!

Hello, as everyone says iPhone 7 / 7+ home button transfer is very common to damage the flex. Apple asked me for 7 plus 220€ to change home button with screen. I make some research and finally found this solution https://www.youtube.com/watch?v=rwznLFI1... I gave it a try because I had nothing to lose and worked. It’s very difficult and complicated, but you should give a try.