Display brightness controls are not working after upgrading to windows 10

I faced the same issue on upgrading my Lenovo G505s laptop to windows 10. This is for non-adaptive screen. I have tried a plenty of tricks to solve this issue. But that didn't workout.Then one day, I tried to update its driver using Device Manager facility provided by windows. Because screen dimming works with Generic PnP Monitors and that needs to be done.Give it a try and let me know if it helps you. I'm using "Lenevo G505s".

To do that go to Device Manager>Display Adapter or Monitors>PnP-Display(Standard) adapter>Right click>Update driver>Browse My Computer>Let me pick from a list>Generic PnP Monitor>Done

Steps to open Device Manager in Windows 8, 8.1 and 10 :-

1. Press WIN + X or right click in left-bottom corner of the screen displayed
2. Press M or click on Device Manager

Now, you will see a screen as seen in the picture below.

Now, double click on Monitors. You will see another screen as seen in the picture below.

I have one display that is with PnP-Monitor (Standard) driver and this doesn't support brightness control neither by control panel's display setting nor hot keys.

To resolve this issue, try the further step. Right-Click on PnP-Monitor(Standard) and click on "Update driver software" in menu.

You will see a screen as shown in the picture below.

Here Click on 2nd Option -> Browse my computer for driver software.

Now click on -> Let me pick from a list of device drivers on my computer.

Now select Generic PnP Monitor and Click on Next. Wait while computer installs the drivers.

Finished and you're done. Hope so it helped you.
Comment in your queries below, if you are unable to follow the instructions.

Thank you.