After myself and a couple of mates had issues playing I have summed up the steps we took to get the game running. If your a steam user and your getting connection failed error then you probably just need to do #4 or #5. 1) Make sure you've extracted all the right files into '[..gamedirectory]\@dayz\addons' and added "-mod=@dayz -nosplash" to the launch options (without the " ") 2) Make sure your firewall isn't blocking DayZ (test by just disabling all firewalls). 3) Port forward the appropriate ports (2302-2307 UDP I think) 4) Open cmd and type in 'netsh winsock reset' (no commas), then restart your PC. 5) Exit Steam, right click and select run as administrator. Then verify the Arma 2: OA game cache. (If one file gets replaced then this was your issue and the game is fixed) 6) Run Arma 2: OA and select reinstall BattleEye anti-cheat. 7) If you have just purchased Arma 2 / Arma 2: OA you must run Arma 2 before you start Combined Operations Hope that helps.