Screen brightness "stuck" on Asus N551JK-DM193H, win 8.1

Hello, first of all I'm not that computer savy, so please keep this in mind! I can google my way around most problems, learning as I go, but this one is giving me trouble. Also, English isn't my first language so I might use imprecise terms, sorry in advance about that.

I bought this new laptop last week, the Asus N551JK-DM193H, and I'm pretty happy with it. It came with Windows 8.1.
I noticed yesterday that, all of a sudden, the fn+screen brightness keys didn't work anymore. There has been a graphic driver update, I can't remember if I was able to adjust the brightness right after that honestly.
I found this forum while looking for a solution, I've tried rolling back the driver but it didn't do anything. Trying to change the brightness manually from the power options or the charm bar isn't working, either.
Also, sometimes the screen dims a bit and then gets back to the normal brighntess.It's quite subtle, but noticeable if I'm on a page/program with lots of white space.

I have pretty delicate eyes, so not being able to adjust the brightness+intense work using the laptop is already becoming a problem. I hope you can help me, and thanks in advance!

(I hope I have posted this in the right category,since I saw similar issues were here)

ETA: graphic cards are nvidia geforce gtx 850m and a Intel HD Graphics 4600 (integrated)

I can only suggest very non specific things to try.

Have you tried doing a proper full restart (not a shut down and reboot).
You could try 'System Restore' to a date when you know it was working.
Finally, as its so knew and if you haven't much installed then doing a factory reset is an option. That will take it all back to day 1 condition.

Hi there! I had the same laptop and the same problem.

After updating the nvidia driver, I couldn't use the brightness keys. I found if you go to 'Device Manager -->Display adapters' and 'enable' the Intel(R) HD Graphics card.

Hope that helps!