How does one see the slider if it is an all white screen? My guess is that you may have to edit a line in a particular file. Hopefully, removing a file or folder will correct this. I have seen others complain of the same and have heard it was actually like mako said the gamma setting was set to max. Also, good luck in AH3 with the GTX950 gpu. Although it appears to be capable of running the game (maybe even quite well) it will not be anywhere near tops in performance.
To give other Nvidia gpu shoppers a heads up. 900 series is rather new only a couple of years old. Performance wise the second group of numbers usually are what to look for (an example my GTX580 was released in 2011, but the performance of my 80 level card could possibly have many advantages to your 50 level card.