Hi,
Windows 10 has completely screwed up my brightness settings. I've updated to the latest Intel drives (HD 4000 driver number: 10.18.10.4252) and it did nothing to solve the issue.
Currently my workaround is:
I've managed to work around this issue by using the fn+ F4/F5 inside the BIOS screen. If you go into BIOS, then you can adjust the brightness.