I played around with the registry FeatureTestControl, setting, and (after trial and error and a lot of googling), Set the value to 0xFFFF and yes, it works! I can now change the brightness using the fn keys
My driver is HD4000 version 10.18.10.3316 (the latest version that 8.1 installs), OS is Windows 8.1
I did confirm that installing the latest HD4000 does overwrite the value in FeatureTestControl. And I did confirm that reverting to an older (windows 8) version of HD4000 does not fix the problem
I still have problems with my touch screen freezing, but I can live with that for a while until Samsung releases a fix. This whole debacle cost me 3 hours today - and a headache from looking at the overly bright screen
----Side Note----
Before I fixed it, I had a chat session with Samsung support over the brightness issue, here is how it went - what a joke..
1. The agent requested a remote session on my PC and searched the registry for the key FeatureTestControl, which was set to 0xF000 (61440)
2. He then told me that the brightness problem was a registry issue, but he cant change the registry as he is only 'basic support'
3. He then opened up a browser on my pc to wea25.com and told me that they would fix it.
4. wea25.com is a PREMIUM 3RD PARTY company that requires a subscription for them to even look at the problem.
WHAT A JOKE.
***EDIT***
Step by step instructions
1. Swipe from right and press on 'search'
2. Type "Regedit"
3. Press F3 to bring up find dialog box (or select this under the menu 'Edit'
4. Find the key FeatureTestControl
5. Write down its current value (So you can revert back if something really bad happens. It will be in hexidecimal format, using the sybols 1-9 and A,B,C,D,E,F
6. Right click, select modify, type in FFFF'
7. No need to save, it already does it
8. Restart
9. Something bad happened? Redo above typing in your original number that you wrote down in step 5, Restart.
CAUTION: If you a following this and you have no idea what Regedit does, then for the love of all and every deity, don't go playing around changing any other values or any other keys. You can really mess things up