Here is the status of that feature and the game: Linear Algebra Abdur Rahman Pdf High Quality Access
The "Checking activation code" feature requires a server connection to verify the license. Unfortunately, the publisher (Activision) and the developer (Gaijin Entertainment) shut down the activation servers for Apache: Air Assault years ago. Depence R4 Torrent Page
Because the servers are offline, the game cannot verify the code, leaving you stuck on that "Please wait" screen indefinitely.