Mouse lag is unbearable, would like help!

Recently bout NS2 and i went in to the game to see how well my computer would run the game. Needles to say, i get about 70 FPS on just the menu screen, but it is impossible to do anything but sit there because whenever i use my mouse, it jerks around the screen and makes it impossible to do anything. It gets worse when i try to go into the training part of the game. I tried some of the suggested things on other threads, but nothing has worked yet. My computer specs are as follows:


CPU: Intel Core i3-3220
Motherboard: MSI Z77A-G41 ATX LGA1155
Memory: Patriot Intel Extreme Master 8GB (2x4GB) DDR3-1600
Video Card: MSI GeForce GTX 650 Ti 1GB
Power Supply: Thermaltake TR2 500W

Any sort of help would be appreaciated.