The problem not in Fn+ keys combination. When I'm trying to change brightness in Windows Power plan menu - seems the same issue, doesn't work... And please read my first message: when I change the 'Display Adapter' settings to Default Windows adapter - the brightness control works perfect!
So, can anybody help me?
I see your system has switchable graphics. It will be better to use the drivers provided by the manufacturer because some of these features are only available with the driver from the OEM. I suggest installing Intel® HD Graphics driver first and Nvidia’s (or any other third party) second.
If the issue persists I recommend contacting DELL* for assistance.
I am having the same issue on a Lenovo Thinkpad W540 running Windows 8.1. I updated the Intel HD Graphics 4600 driver to the latest on the site (10.18.14.4080) and still no luck. Going through Charms -> Settings -> Brightness doesn't work nor does the hardware brightness buttons. I am however able to adjust it using the Intel HD Graphics Control Panel.
Intel HD Graphics 4000 and Windows 10 & Windows 8.1 ( Brightness fix with latest driver)
Brightness Fix with Driver Date 8/17/2015 )
Brightness problem Solved
Intel HD Graphics 4000 with NVIDIA® GeForce® GT650M graphics.
Intel HD Graphics 4000 Driver, Driver Date: 8/17/2015
Driver Version: 10.18.10.4276
Make sure you backup your registry first before proceeding!!!!
open regedit in Run Command
Registry has wrong value:
Currently reads as :
"Edit DWORD 32 bit"= f000
Registry with New Value:
You needed to change the value in registry to: ( f008 )
"Edit DWORD 32 bit"= f008
Then Restart Computer
Brightness Fixed with Latest driver.
Let me know if this was helpful to you