Yes, I have already tried turning off adaptive brightness in the power options, and tried to use fn + a, turning off Display Power Technology. It seems that only turning off Display Power Technology works, however, it goes back to auto dimming even though it is turned off after restarted the laptop a few times.
It also seems that this is an issue with some Asus laptops, where they did the above mentioned but it didn't work either
Since you created a new thread, rather than posting on the one you were reading, there is no way for us to know what instructions you are referring to.
That said, when you checked and turned off adaptive brightness, did you reboot after? Some devices need that. And you need to make sure it is turned off for both when under charger or battery power. Lastly, you may want to go into "Control Panel" > "Power Options" > "Change plan settings" > "Change advanced power settings". Check the settings for all the options in there, as they can effect it.
Question though, is it dimming just all the time (when you are using it) or only specific times, like when charging or when running on only battery (no charger connected), etc?