Mouse input lag, cannot shoot or aim down sight while moving/(using keyboard).

Hello, 

I have encountered mouse input lag, everything i use my keyboard like WASD or any key with my keyboard, i cannot aim down sight/shoot at all. The mouse can still look around, but just unable to shoot. I need to not use the keyboard, for like 1-1.5sec  only i am able to shoot or aim down sight. 

Any fix to these issues?