This is not a question but a solution.
I have Toshiba Satellite C660. When I use to install wins 10 on it. The Fn keys were working expect the brightness up/down. but right after 1st drivers updates the Fn keys use to stop working. Basically the problem is caused by Dynabook drivers. I uninstalled the two dynabook from System devices and one Keyboard driver (i guess the Keyboard Driver was the culprit). Then All Fn keys are running perfectly fine.