At the main menu press LT and RT untill stood up.
Then walk over to the computer and type in the codes.
The computer is behind the chair.

In order to access the terminal, Mason must be out of the torture chair. Once hes free to walk the room, head over to the left and press X or Square for access on the Terminal.

Enter the following cheat codes to unlock the following:

UNLOCK ALL INTELS By entering the code below, players will be able to unlock all intels and let them view it. Please take note that by entering the code, the process in unlocking the achievement or trophy will be disabled.

Code: 3ARC INTEL

UNLOCK ALL LEVELS, ZOMBIES LEVEL, AND DEAD OPSTo unlock all levels in the campaign, zombie and dead ops mode, simply enter the following code.

Code: 3ARC Unlock

PLAY ZORK
Simply enter the code ZORK in the terminal.

Have Fun!!!