Second hand game

I believe you are referring to Dead Ops Arcade. Here's an explanation I found of how to access it.

Accessing it isn't just a matter of finishing the game. You've got to bust your way out of the main menu screen, then work your way around to a terminal and type in the correct commands to boot the game.

While in the menu look down (using the right analogue stick, presumably) at your hands and mash the triggers to wriggle your hands until they come free.

You'll stand up and be given the freedom to roam. Go to the terminal, access it and enter CD, then DOA. Bam - giant machine guns, flame throwers and rocket-firing bats are yours for the shooting.

It seems like your problem is a common one. Unfortunately the PC latency has been very bad for a lot of Black-ops players, and by the look of it it is even worse in Brazil.

Are you behind a firewall or anything that would limit your connection speed? Does a port need to be forwarded on you router? How has your connection been lately on other things? (movie streaming etc) If the network in your area is one that experiences heavy load it could easily take a toll on your bandwidth. You could also go through this ping boosting guide and see if any of these help you.

Let me know if this helps.