Alright i had this problems but i done those steps and it worked : Install Arma 2 and Arma 2: Operation Arrowhead. Close Steam completely, and then rerun it as an administrator (this is required to launch Arma 2 for the first time. You'll get a bad serial key error otherwise) Create folder called @DayZ in C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead Create a folder inside of that folder called Addons, and then download all the DayZ mod files from the DayZ website into that folder (So they should be located in C:\Program Files (x86)\Steam\steamapps\common\arma 2 operation arrowhead\@DayZ\Addons) Extract the files into the Addons folder. Make sure they are in the top level of the Addons folder or Arma 2 won't be able to find the files. Launch Arma 2 (you need to run Arma 2 first in order for Arma 2: Combined Operations to work, which is required for DayZ. Launch Arma 2: Operation Arrowhead from the Steam library, and run it as Arma 2: Combined Operation That's all you'll need to do to get DayZ working. Chances are you'll want to filter out the non-DayZ games, which you can do by opening the Filter menu and setting mission to DayZ.
