I have installed the latest driers and since then I am unable to change the screen brightness using function keys. I have installed multiple driver updates hence it is difficult to find out which driver is causing the issue.
Any pointers in this regards would be a good help.
It seems the newest Intel HD driver (from Intel) is causing this issue.
Please uninstall it and reinstall the driver provided from Lenovo.
The drivers can also be downloaded from the link from table below. Alternatively you can go directly to the Lenovo support site download the drivers which may have more latest drivers.
Intel Display/VGA driver for Windows 8 (32-bit, 64-bit) - Desktops, Notebooks (Windows 8 Inbox driver) ... Learn more
Windows 8 32-bit Windows 8 64-bit
Intel HD Graphics Driver for Windows 7 (32-bit), Vista (32-bit) - ThinkPad ... Learn more