shift-reboot and choose smth like "don't check drivers signatures" at startup menu
Boot windows
Install driver
go to device manager, right click on your gpu, disable it.
reboot to safe mode
replace atikmdag.sys
open the signing tool "
http://www.ngohq.com/?page=dseo" and sign that file.
open admin cmd window and type "bcded /set TESTSIGNING on"
reboot
Device manager, enable GPU again.
Done.
Thank you, guys, both ways work.
In my case I even did not need to disable/enable gpu, I just signed that mod driver and it works well after reboot.
It works well on win10 and on win7.