The original poster is not alone with this dilemma, though I cannot say when it started for me. I have an HP 15-g035wm that has developed the same issues. I have disabled the "Action Keys" feature in BIOS, but all that does is require me to push Fn along with the function key in order to get it to do its noted function. I work with software that employs the function keys, so I need them to behave like function keys normally did, which means doing nothing unless Fn is pressed with them to trigger the "icon function." All of the other functions, e.g., mute, volume up/down, Airplane mode on/off, etc., work just fine but the brightness up/down buttons are not functional and I can find absolutely nothing in "the usual places" for a brightness slider for the display anymore.
If I use a program such as f.lux, it is still able to adjust the screen settings, and I even tried making sure that it did not start on system startup since I thought it could be interfering, but it isn't.
This thing has an AMD A8-6410 with AMD Radeon R5 Graphics. The AMD Catalyst Software Suite was added after the upgrade from Win8.1 to Win10, but I didn't notice any disappearance of the usual Windows based slider controls at that time.
I'd love to know just what's up, and I wonder if "what's up" is with Windows 10 or not.
Edited by britechguy, 14 February 2016 - 11:35 AM.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
In a modern society where everyone thinks their opinion deserves to be heard nothing annoys me more than individuals who mistake their personal preferences for fact.
~ Commenter TheCruyffGurn on the The Guardian website, 8/13/2014