I reinstalled the game (Assassins creed revelation), and wrote the old key to the game. The key was invalid. What do I do? Can I disable the password?
No you cant. It's because of this I stopped gaming on PC's, as soon as you get a new computer non of your old CD keys work!
You just need to use the account you had when you first activated the key. The game won't ask for the key again and you will be able to play as before.