Yes, I never played, only for the tutorial, and I would like to play... can you help me?

Hi guys, I'm a new player on tanki, and I want to tell you my problem on it: when I'm in the login screenshot, but if I put my username and password, I can't press on Play button, is as if it's blocked, can you help me? Ah, I tried with more browsers, such as IE, Mozilla, Google Chrome..but nothing gives me the same problem :-( http://i60.tinypic.com/34qtz4w.jpg