i have bought sime3 at launch several addons later on

Once you register your discs orgin has a copy of your game in download versions with the serial numbers. You have to download origin to play the game

You need to download origin, open origin at desktop and there you will find download verions of the game. Run your mouse over the game and click on the title will take you to your registration code.

https://www.origin.com/en-us/download