Re: my sims wont let me play,keeps asking for a code i used when i instaled it..

Don't stress, you bought the game it's yours to play. I'll try to help you find a way to play the game, and if I don't succeed EA will. 

Try this:

When starting my game from the shortcut, the game asks for my serial code again/asks me to activate the game

This usually happens if you are logged out of Origin for some reason or if there was an Origin Client update. Don't use the shortcut to start the game if this happens but log into Origin first (use your Email address) and check if the game still properly shows up in the My Games tab within the Origin Client. Do any necessary Origin and Game updates and then hit PLAY in Origin to play the game. 

Source: http://answers.ea.com/t5/The-Sims-4/FAQ-Serial-Codes-Game-Activation-and-Download-Issues/td-p/4228232