I upgraded my Sony SVF15A13SN -- which came with Windows 8 out of the box -- to Windows 8.1 yesterday, and have been unable to change my screen's brightness since; it's stuck on maximum. 

I could change it just fine until yesterday. The brightness setting in the Settings Charm is unavailable (greyed out) now, and says "Windows can't adjust the brightness on this display" when I hover my cursor over it. 
The Fn+F5/F6 is also doing nothing. And I mean **nothing** -- I keep reading about people whose Brightness sliders move up and down while having no effect on the brightness; in my case, those buttons do nothing at all.

For all the lazy people out there who don't want to look up what hardware I'm sporting, it's an Intel® HD Graphics 4000 and an NVIDIA® GeForce® GT735M.

Now, these are the "solutions" I've found online:

* "Update Intel driver"

Tried it. Didn't help.

* "Roll back to previous Intel driver"

Tried it. Didn't help.

* "Switch to basic display adapter"

Tried it. Didn't help.

* "Disable Intel adapter, restart, Enable Intel adapter, restart"

Tried it. Didn't help.

* "Update NVIDIA driver"

It's up to date.

* "Disable adaptive brightness"

Tried it. Didn't help.

So.

What next?