help me play cod2

[gbsachs]

hellou, i really wanna play cod2, i downloaded the game( its a 3.5 giga iso- whatever that is), installed it put a cd key, from the key generator and like all other 15 games i downloaded, it doesnt work, i mean it accepts the cd key, installs it succesfully and then when i try to put the game, it says: put the coorect cd rom and sheet, why the [bleep] does that happen, i downloaded anything that says: cod2 game crack, game patch , mds,((whatever this things are) and i dont know what else, and it doesnt work, this happens with quit a few games.
my questions are why?
how do i play these games and especially cod2?
my kingdom, my [bleep], my mother to clean your house and my awsome collection of [bleep] for an answer