Extra prompt window in login

Hi!

There is something wrong with the login. When i press “login” There opens a prompt window which does not get me in, even if i have correct credentials.
BUT when i press Cancel two times, then it will open that page to URL /wp-login.php?redirect_to=%2Fsitename%2Faddress%2F
Which has WordPress login page (without CSS though…) and the same credentials work there fine.
So how can we skip that prompt window, which is not working at all…