Open the terminal and follow the steps:-
a). sudo touch /user/share/X11/xorg.conf.d/20-intel.conf
b). sudo gedit /user/share/X11/xorg.conf.d/20-intel.conf
c). Type the following lines

Section "Device"
         Identifier "card0"
         Driver "intel"
         Option "Backlight" "intel_backlight"
         BusID "PCI:0:2:0"
EndSection