i have same problem after upgrade graphic card iris intel. downgrade with the driver 27.20.100.8680 and it's work with reboot.   Please dell work for resolv problem !!!
I am not able to change the screen brightness in my laptop, I tried all the solutions available online. But, didn't succeed. Actually, this happened before too, I updated the drivers and everything was fine until now again. I have no idea what is happening and it is very annoying when you can't change your brightness. It would be extremely helpful if someone solves this.  
Can not adjust screen brightness Inspiron 14 7000!