Most mouse have on-the-fly sensitivity I have a 2000dpi setting and 800 and 400 setting. I use 800dpi. There is an option in my mouse settings to have mouse acceleration turned off in game. I use acceleration in windows but off for games. If u have a new mouse it might be something simple like thing or the fact that you have not scaled the onscreen movement down enough to cope with 2000dpi if you are set at that all the time.
If thats correct i think thats the problem, so how do i enable for windows only, and not in games.
What is actually the difference between DPI and sensitivity?
I use a Microsoft IntelliMouse Explorer 3.0, so it's whatever that comes with.