Ensure you have a clean installation of the latest Arma 3 version.
This usually means the server version does not match your game version. Ensure you have downloaded the latest patches corresponding to the nino23 update. arma 3 mp cracked steamworks fix nino23 link
Ensure the Steam client is running and you are logged into an account (using a "dummy" or secondary account is highly recommended). Ensure you have a clean installation of the