Serious problem over online gaming

ok heres the problem i got broadband a few months back no every time i try to play a multilayer online such as doom 3 ,prey, fear or halo i cannot connect to the servers for gaming. now on dial up i can connect but obviously i can't play because of lag. but when i am on broadband i cannot connect. the modem that the installed to my pc just stops blinking the service provider provided a pradyne modem and the connection is always on requiring no login but i can't play no multilayer in my games but if i load a game such as hero online i can play but i want my fps to work especially fear combat i can see the servers but cannot connect. yes i can seee the servers for some games like fear halo but i can't connect in games like prey and doom and quake 4 i can't even see the servers. i even have my firewall allowing the games and i even disable the firewall but nothiign works anybody know what can be done. i am tired with this any help appreciated

some of my friends got the same service and they can play somehting on my system or moden is blocking it