Go to the main menu screen where you're sitting in the chair facing a TV screen with the words "Campaign, Multiplayer, Zombies, and Options" written on it. Press LT, RT, LT, RT, LT, RT over and over, as fast as you can, until you break free from the chair. Now make your way to the computer which is located behind the chair.

Once you're at the computer, enter the follow codes:

doa (This will unlock Dead Ops Arcade)
3arc unlock (This will unlock "Five")
please +rep