Hello,

thank you for the feedback.

Could you please describe the issue you are experiencing a little bit more?
Does the game start loading or it doesn't start at all?
Does any error message or warning pop up when you try to start the game?
Does the launcher start? In case it does but you are not able to launch the game from the Launcher, did you try running the game directly by starting the exe?

In any case, first thing you should try is to verify integrity of the game cache via Steam.
Steam > right-click Arma 3 > Properties > Local Files tab > Verify Integrity of Game Cache.

Please let me know whether the verification have helped.

Thanks