Phone boot / startup problem

[Archanos]

I have a problem here with Z1, ofcourse I didn't root it or something. Clean, stock phone, bought without any branding.

Every time I turn the phone off, I cannot make it to start again until several attempts.

It turns on, shows the Sony logo, flashes to show the next XPERIA logo but it never happens. I see backlight is on at 100% brightness, but there is no boot animation for about 8-10 min. After that it shows the animation, starts to the home screen, but backlight stays at 100% brightness - I cannot manipulate it anymore, even If I use power buttn, screen contents goes away but light stays on at full swing (black screeen but with backlight).
I tried to toggle then the "Optimized backlight" option in the settings, but then screen goes completely dark (SOD issue known from Z Ultra).

On the other hand, if I restart the phone successfully (after several hard resets with the red button next to SIM card), everything works OK. It takes around 5-15 attempts to make it start fast and without this problem.

What should I do to make sure when I turn the phone off, I can turn it on without this silly fight?

[Urban-Ghost]

I have same problems, i plug the charger in, the red light comes on and the sony logo appears after about 20 secs, it dissapears again after a few seconds and then does the same thing al over again, i plugged in the laptop and it did the reset thingy but would not switch on after that, but as soon as plug charger back in i start all over again, I have changed chargers but nothing works, any help is appreciated.