I need some help with a PC gaming issue

Hey! I built my PC a little over a year ago now. I am having this consistent problem in my PC gaming experience that is making it difficult to play my games. Whenever I play a game, everything in the screen "skips." I don't really know how else to put it. Using fraps it says my frame-rate is perfectly fine (Max Payne 3 runs at an average of 60fps, yet it is the game I play where this issue is most noticeable.) I first noticed this when I kept messing up my aim in shootin games. The aim crosshairs would skip around, almost like I was having high latency in a multiplayer game. I was extremely frusterated with this and assumed my Razer Deathadder was the cause. I then proceeded to switch the mouse to an old shitty wireless laptop mouse just to make sure the mouse was the issue. It wasn't. The problem still persisted even with another mouse. I was then playing GTA IV when, upon further inspection, the whole game was doing these skips. Citizens would just walk around like a chunk of their walking animation was removed. This happens in every game I play. It renders third person shooters near impossible to play, and ruins the experience in first person games. So far, I have tried to update the mouse and video drivers, and format my hard drive, which did nothing. When I tried watching a movie on my computer, the problem did not seem to exist. Please. This problem is extremely frustrating and I'm desperate for a fix. Any help would be much appreciated. Thank you in advance. My specs: GPU: Radeon 6950 2gb. CPU: Phenom II x4 965. Ram 4gb 1600mhz. OS: Windows 7 64-bit. Psu: 750w.