you can't use disks with steam nor origin with steam steam versions only work with steam origin and disks work together you can do it the other way around use the steam key in origin but you'll need to uninstall the steam version
hang on there is a guide here *note to self bookmark guide for future reference* will edit this post in a few
edit to add link http://answers.ea.com/t5/The-Sims-3/FAQ-Steam-VS-Origin-VS-Discs/td-p/3135440
also make sure java is up to date and flash player and if your getting looping while trying to register on the account try clear the internet cache and or switching browsers if using safari,opera or chrome try IE or firefox
