Laptop display is dimming automaticklly after login

lundi 8 août 2016

Hello,
I have installed the OS updates from Ubuntu software center. When I login on my laptop after ~minute the display is dimming to 50% then 100% and can do nothing about it.
When I have a second monitor connected to my laptop (mirroring or extended desktop) the same thing happens with my laptop monitor, but the external monitor is working.

Any help? Can't find a solution on google.