On analog VGA

Open Right-Click on Desktop and Click on Personalize.
Then a Window will open-up with desktop Pictures.
Here Click on ‘Display’ Option listed in the Bottom-Left corner.
In the next Window, Click on ‘Adjust Brightness.’
Now You get the Final Settings to Adjust the Brightness of the Computer.
Slider the Meter beside ‘Screen Brightness’ to increase the Brightness( it is situated at Bottom).

HDMI and DVI will not have gamma settings.

Brightness is only for Analog Displays

hmm, I have windows 10 and I seem to remember for a desktop (not a laptop) the brightness settings are not there, as in you do that on the monitor itself.

If you have an add-in video card (eg NVidia or AMD card), open the card's control panel and change the settings there.

If the control panel doesn't display its icon on the right end of the taskbar, you can probably find the control panel by pressing Win+R and typing in: control and pressing Enter.