Still cant play Cod 4 online

Hello,
wonder if you can help, cannot get onto COD 4, have read all of the advise about the router but cannot do this as the router is shared with the computer, my brother's xbox and my other brothers PS3, they both work fine for it, have the problem that sometimes it will work, sometimes I have to reset all of my internet settings and it will work but mostly it wont work at all..


HELP PLEASE!