If you are running the game on modern hardware (Windows 10/11), you may encounter technical hurdles beyond activation:
The PC version originally used Solidshield DRM, which required a digital "handshake" with Ubisoft’s servers. Now that those servers are dead, the game remains locked even if you have an original disc or a legitimate serial key. Offline activation serves as the only way to bypass this permanent lockout. How to Complete Offline Activation James Cameron 39-s Avatar The Game Offline Activation