My character keeps walking backwards

hi there!
i got a problem that i already tried to solve with steam support, but they sended me to this forum.
 
when i start OMD 2! the mouse keeps scrolling downwards without even touching the mouse.
and when i start a game, my character keeps walking backwards and i cant control it.
 
i already tried to do "verify integrity of game cache" but it wont work.
 
then i have almost the same problem with Left 4 Dead 2. in this game my mouse isnt sliding down but  the character im playing walks backwards, the same as in OMD 2.
 
i really dont know what to do..
please help me! :)