I have this issue on my Dell Inspiron 13 7000 series for very long time. I tried searching Google and Dell support community and I did:
Control Panel > Device Manager > Display Adapters > Intel HD Graphics 5500 > Driver > Update Driver > Search Automatically.
18:35 on 25-Dec-2016: Sorry bro, I did as above; it fixed but when I try pressing the brightness button then It come back problem again: can not adjust the brightness. Hic hic
19:00 on 25 Dec 2016: I even try downloading and installing the latest Intel Graphic Driver (issued on July 2016), but just after a while, the screen comes back very dim.
I accidentally discover this: Setting --> Display --> uncheck the box "Adjust my screen brightness automatically".
Sorry, but stupid Windows!!!!