i have EXACTLY the same issue. also have nearly same pc as you... croe2duo, 4gb ram, and AMD-ATI....
i was able to play in windows 7. but in windows 8.1 i always get the disconnect after the loading screen. after loading the screen goes black(with cursor on top right) and stays for a few second, then quits. in windows 7 that black screen with cursor only shows for a fraction of a second and im in. i know if i see this black screen longer then 1 second it will not work.
i always did clean istall of win 7 and 8.1 (no upgrade). i reinstalled 8.1 about 3 times.. never had luck.. on win 7 its working just you know.
ocasionally i manage to get on servers ()in 8.1).. i would say 1 out of 20 tries? which i also find rather strange.
thanks for the tip to try unranked servers without PB/FF. i also can stay on server without PB. thats very interesting news for my situation.
