Can not make @-sign on the sims 3, so can not log in. Help!

Are you talking about the game, or some website, and which one? What happens if you try to type an @: does it not register, or do you see a 2 instead? If so, try using the other shift key—the one you've been using might not be working.

When you say copying and pasting doesn't work, how are you trying to do it, and where does it not work?