Had a very strange event happen tonight and I saw a lot of posts about it without a lot of resolutions.
After I installed the Windows 8.1 update, my brightness control was set to the lowest setting and updating it didn’t change the level.
It was a simple fix, so I’m not sure why so many people were having problems with it. I went the Lenovo download page and re-installed the video drivers for Windows 8. It did tell me the drivers I was installing were older than the current, but I clicked through that and viola, it worked!
I think the fact that it tells you you are installing an older driver might be throwing people.