When I enter my Sims 3 product code it says ''This code has already been used''.

If you are using mac the customer service days to update your system with the os x yosemite software..and also make sure your system is up to date prior to downloading...if all else fail contact origin, they were very helpful witht the install portion and even told me if we could not solvethe issue then we could talk about working out a refund...online download purchase (not store buy)...hope this helps