1) Go To main menu
2) look down till you see your hands
3) Rapidly left and right click while also tapping the spacebar and you will break out of the chair ( you will receive an achievement)
4) walk behind the chair you where sitting in
5) access the computer that’s behind you
6) type DOA
7) Black Ops Arcade will come up and just watch the cutscene it gives you and the achievement will unlock.
Note: This will also unlock Dead Ops zombie level for you to play!