Well Im banned at the moment so Im in no better situation, but I can help.
I'll assume the disc is clean and that you bought it form a trustworhy shop and didnt copy the disc? If any of the above arent true then that could be what it is, but otherwise it could be a memeory problem. Delete any loose files on your xbox/ps3. It could otherwise be an etching problem on the disc.
When MW2 was first released, there was a big problem, where batches of games that are bought by shops had etching problems (when the data was being burned to the disc, their was an error which caused the disc to be unreadable to a certain level, for example, it works until you select multiplayer, then the disc unreadable sign appears). There is another problem which I cannot remember, but you should do a Google search on "modern warfare 2 multiplayer not working" or "modern warfare 2 disc unreadable". Have a look at a few pages on there and you will see that many people have had some strange problems. Hope this helps, I had this problem with MW2, I know how you feel.
There are no cheats
There are no zombies cheats.
You look it up. It works to.
you can but don't do it man"!"
ZOMBIEKILLZ gives you unlimited ammo in any zombie map
go onto gamezone they have cheats and everything
No you can not be a Zombie.
You can download USB mods, but there are no ingame cheats. And USB mods can potentially get you banned from PSN or Xbox LIVE
I know some cheats. 3arcunlock all 3 zombie maps, hello sailor, 3arcintel, alica I'm not sure if this one works but its supposed to be some game.
just play the game ?
Black OpS cheats help you win the game!!
I don't know many but I know 3ARC UNLOCK will unlock all levels including five, a zombie level. And DOA unlocks an arcade version.