Can't change Brightness level on HP dv7-6179

Im using Ubuntu 16.04 LTS. Before I could change the brightness with the key combination:

"fn" + "f2" to decrease

and

"fn" + "f3" to increase

But now, it only changes the bar in the right upper corner... but it doesn't affect the brightness of the screen...

I've tried creating the "20-intel.conf" file in

/usr/share/X11/xorg.conf.d

but when I logged in again, there was no change...

I've already tried with the "Brightness controller" and it works... but I would like to know if there is a way to "reset to defaults" those keys "fn" + etc... before reconfigure it with xbindkeys.