Brightness buttons stopped working Win10

Hi sushisan,
I am Vijay, an Independent Advisor. I am here to work with you on this problem.

I am not sure whether a repair upgrade of Windows will help but seeing the situation, I would suggest that you uninstall the latest KB update and hide it so that it doesn't install it automatically and wait for new update to come which will be installed automatically.

To know which update got installed
Windows Key+i to invoke Settings > Update & Security > Click View installed update history. These KBs should be from the below list. Don't uninstall any other KB
For 1****
Make note of KB and uninstall and block it.
Uninstall
Windows Key + R > Type: appwiz.cpl > Enter > Click View installed updates > Select the required updates, right click, uninstall.
Block
Microsoft has provided a tool Show/Hide Updates tool to block the update
Download the tool from below link
http://download.microsoft.com/download/f/2/2/f2...
When you run this troubleshooter, it will search for available updates and list them
Select the update which you want to hide. Click Next and follow on-screen directions

Do let me know if you have any more question or require further help. If above didn't work, I will supply more troubleshooting steps to solve this problem.

Hi sushisan

I am Sumit, an Independent Advisor and a 2-Year Windows Insider MVP here to help.

Do you know the update which caused this?

Please see the below options:

Option 1.Try Rolling back if you have an option:
Go to Device Manager by typing in Devmgmt.msc in Run dialog box.
Navigate to Display devices and right click ATI Radeon HD or Similar device you have. Choose Properties.
On the Driver tab, hit rollback Driver to go back to the previous version.

Option 2. Remove drivers completely and Install the the newest ones available from the OEM or the maker.
What you need to do:
1. Uninstall everything of Display driver using DDU
http://www.guru3d.com/files-details/display-dri...
2. Reboot.
3. Make sure your device manager shows Microsoft Basic Display adapter.
4. Download the driver from the OEM or the maker like AMD
5.Run the Setup and you should be good to go.

Disclaimer:
Guru3d.com is a non-Microsoft website which would provide accurate and safe information. Watch out for ads on the site which are frequently classified as a PUP (Potentially Unwanted Products). There is no need to buy paid products to fix your computers as they do more harm than good sometimes.