This is driving me mad, and it drove me mad last time and I can't remember how I fixed it.
I have just installed windows 8.1 on a new PC with an LG 22EA53 monitor and Nvidia Geforce 650 Ti. I don't know which of these is causing the problem but my screen keeps changing brightness depending what is on the screen and it is driving me nuts.
I had this problem on my old PC but I cannot remember the solution or if it happened on purchase of win 8.1 the GFX card or the monitor.
I have tried several solutions from Google and none have worked.
I have tried: turning off 'enable adaptive brightness' in power options (was already set to off)
disabling almost everything to do with the gfx card on startup
checked every menu I can find on the monitor
and a couple of other things I have forgotten.
I know this can be fixed as I did so with a solution I found through Google on my old PC, but am having no luck and am hoping one of you can please save me!