The 125hz doesn't work anymore ?

Hello, i took Crossfire for a while and i know that before everyone play in 125hz with the mouse, but there when i am in 125hz my mouse is messing around and my viewfinder is not stable, is this normal ? Do i have to modify something or it is no longer possible to play in 125hz ? Because i saw that you could play in 1000hz but i prefer to stay in 125hz as in the old way.