Right click on your desktop, and select Properties. Go to the Settings tab and click the Advanced button at lower right.
The top right tab of your new choices should be your video card setup. Click on it and find the section that contains vsync. I dont know exactly what your setup is, you'll just have to go down the list until you find it.
If you have frame rates at 120 I can guarantee its off. The problem is what you actually see on your screen (frames per second) is limited by your monitor's refresh rate. In your case, its 85. So you physically will never see more than 85 fps no matter what your video card says it is putting out. Vsync attepmts to put your video card's output "in sync" with the monitor's refresh rate, and shows you realistic frame rates. Without this enabled, the video card can get way ahead of a slower system and cause freezes and stutters on your screen.
I'm not saying this is your only problem, but once you have realistic frame rates and you dont have to worry about stutters or freezes caused by this, other problems can begin to be ruled out.