Hi,
We are aware of this issue:
Some players have reported that after recently downloading and installing specifically Battlefield 3, the first Crysis, Mass Effect 3, or Plants vs. Zombies, that their game does not activate in their Origin My Games list.
We're investigating this issue and are working to get you back into your game as quickly as possible.
Thanks for your patience and stay tuned for updates.
We are hoping to provide an update soon. In the meantime, please stay tuned to this article here: http://help.ea.com/en/article/some-games-wont-activate-in-origin/
Cheers,
Nils