@Saskia4 That's normal for the first time you load the game: you're in the tutorial, which doesn't give you the option to choose a household. This also happens when you have a new options.ini file, which you would if you had a new Sims 3 user folder or were installing the game for the first time on a new computer.
If you don't want to play through the tutorial, click the three dots in the lower left corner of the screen, select Edit Town, and you'll be asked whether you want to exit the tutorial or not. Once you say yes, you can click "return to game setup" at the top of the screen and get the normal options.
