How To Register Sims 3 Bought Online I Can't Register My Sims 3 Game :(?

I can't register my sims 3 game :(? - how to register sims 3 bought online

I can not register online, which does not accept my serial number, the game is not new, I've had for some time, it is first installed on my laptop, then moved to the 'KINGDOM and has a new desktop PC and installed Vista again but can not be registered in one of the computer! says my serial number is invalid, which is a shame, because I want to buy things there.