Hello Mustafa,
good news - problem solved! It was a hardware issue indeed. Apparently all it took was to enable lid switch in bios settings, which for some reason was turned off as default. Once I enabled this option, everything started to work like a charm, and what I set in the control panel finally has some influence on what the computer actually does.
I decided to post it here because someone may find it handy in the future. All you need to do is turn on bios when starting the computer, go to 'Power', enable lid switch and press 'apply changes'.
Kind regards
Mary