If you own the original DVD case, the CD key is typically found:

The DRM allows 3-5 installations. You (or a previous owner) have installed it too many times. The Fix: You need a "revoke tool" from Ubisoft support. Since support for Fatal Conspiracy ended in 2018, you are out of luck unless you find a crack (more on that below).

Now she just needed to survive the conspiracy.

Common mistakes include swapping '0' (zero) for 'O' (letter) or '1' for 'I'.