Ideapad Z400 Touch Win 10 Brightness Problem

Step:

1. run Regedit

2. Find

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class\{4d36e968-e325-11ce-bfc1-08002be10318}\0000]

and

[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Class\{4d36e968-e325-11ce-bfc1-08002be10318}\0001]

3. Add paramiter"FeatureTestControl" in key 0001 and 0000. 
Choose dword32. 
Insert value:0000f048

4. Reboot