On chaos theory cant get internet multiplayer to work as it asks for a code but dont know what code is ?

That problem needs to be directed to the Technical Help Forum.

Your game should have included two key numbers. One is for installing the game and the other is the one you want for playing online. The online key was on the back of the manual in most cases. It is unique so you cannot use somebody else's number. If you are missing the number (it begins with "SC3-****), you will have to contact UBI customer service and prove you have a legal copy and they may be able to provide you with a number (I don't work for them so I can't promise you they will, but if you don't have one, it is your only chance).

I think the game is genuine the box and manual look real same with cd itself but there is a white box at front of manual with nothing in it.

You will have to contact Ubi support then.
http://www.ubi.com/us/support/default.aspx