Hi
I have Windows 10 Pro on HP Pavilion PC.
Although I haven't read all the responses on this thread it appears there has to be a compromise in terms of energy saving or a fix has to be downloaded, or the Catalyst app has to be downloaded or a change to a service etc.
In my experience which I have just tried and it has resolved is as follows. This is based on Windows 10 Pro however it seems to be the same desktop app as previous versions of Windows (down to Vista at least I think).
Open up Power Options from Control Panel (if category view then its System and Security then Power Options).
Firstly click 'Change advanced power settings' button
Scroll to bottom and you should see ATI Graphics Power Settings, press + and you will open up ATI Powerplay Settings, press + and you will be able to change 2 options. On battery: and Plugged in:
Change both these to 'Maximise Performance' and click 'Apply' at the bottom of the window and then click 'OK' to close the window.
Now you should be able to adjust the brightness slider bar for the 'on battery option'.
Save changes and reboot the computer and this should resolve the problem as it did with me.
I would be keen to know if it has resolved the problem and should it re-occur it is worthwhile noting what updates to either Windows or your laptops manufacturer has happened.
RobD1Headshot