Sims3 Origin Produktkey

hi, i installed my new sims 3 starter pack on my computer but my cumpture is very slow and it takes hour to only make my sims. so i uninstalled it. my boyfriend told me to installed it on his computer because it is way more powerfull them mine but when i enter my key product code it says it has already been use. what do i do. i really want to play my game but i cant with my computer. can someone help me?