Fandall

So, hello. im kinda new to this all and ive just downloaded arma 2 free version. The thing is, when i try to enter Dynamic zombie sandbox server, i get to the loading screen and then the game just freezes ( i mean, it's still running and i hear some birds and wind, but i have a screen where i see a gun, few zombies and all blury ) I asume that thats loading screen but, well, whats the problem? Why cant i get pas that and into the game itself?