Having the same issue here, no controller, joystick, or anything plugged in. Pretty sad that I am completely UNABLE to play the game due to this issue.
I am also having this trouble with my character looking down in game. if i invert the controls then he looks up. if i disable the mouse look and set look to a key it does not change anything. just stuck looking up or down. i can turn side to side and shoot, so it detects the mouse. i tried a different mouse, and it still don't work. i cant find a single solution to this problem. and i play 30 other games right now on my PC and no mouse issues.
