Before upgrading to Windows 8.1, I install Windows 8 64 bit with driver and tools in the following list: http://www.asus.com/Notebooks_Ultrabooks/K45DR/#support and windows 8 work properly, including brightness control.
After I upgraded to Windows 8.1 with the same driver of Windows 8, Windows 8.1 brightness control does not working. I installed Windows 8 drivers for Windows 8.1 because Windows 8.1 driver is not yet complete on the web.
Drivers have been updated, but still does not working.
Specifications my notebook : Asus K45DR A8-4500M Processsor, AMD
Radeon® Mobility™ HD7640G + HD 7470M Dual Graphics with 1GB DDR3 VRAM
This problem is very annoying me Please help to fix the brightness control on windows 8.1 64 bit