Hi @QueenMurkem
You may just need to re download Origin because of various updates but, depending on the situation the solution to this may vary.
See the full EA article here
If you have already registered the game yourself and are trying to reinstall the game
The game does not need to be registered again. Login in the Origin Client with the Email/PW you first registered the game on and download and install the game from there. The game only needs to be registered once and you won't need the code again after your initial registration. This is true for both the DVD and the download version. You can skip the activation step on reinstalling.
If you bought the game on Origin
If you bought the game on Origin, it's not necessary to register the code anywhere. Download the Origin Client here: http://origin.com/download, login with the same email you bought the game with and find the game in the Game Library tab within the Origin Client to download. You don't need the serial code.
Also try:
Restart Origin.
Log out and back in and use the email address instead of the username. Make sure to use the one you used to register the game in the first place.
Reinstall Origin.
Restart your router/modem.
Make sure the game isn't hidden by accident. To check, put the filter to Hidden Games. If it's there, right-click on the game to unhide
Hope this helps,
Sasha