I know how to fix this there is 3 diffrent ways!

1. throw ur router out the window and use ur cable stright to the wall.

OR

2. find the router in my computer and right click it and there should be something like add in there put name: Starcraft Port from: 6112  port to: 6112 or something like that.
(u have to do this quite often) it like disapears sometimes when u restart..

And then u have to go to regedit and add a line there cant remember what but something like portmapping 6112 in bnet folder. Google it. (there are like 3 bnet folders think it was current user)

OR

3. Check your firewalls. I recommend u try step 1. first and see if that is the problem and then step 2.