''Error durning initialization: Steam must be runnin for initial authentication to succeed. Please start Steam and restart the game to continue.'' I tryd trought steam to but still same. Am I doing something wrong or I am just dumb ?

You don't have MW3 bought. Buy the game and start steam or create a folder called "dw" in the mw3 folder it would help you bypass the check. also, i never told you this.

create a folder named dw inside your mw3 directory

Got it thx alot !