My dad was the one who fixed mine so ill just tell you what he did, and if it doesnt make sense, i cant help, sry:
I found out the ip of my playstation(i didnt know the ps2 had a seperate ip than my computer until i did this) by playing Tribes: Arriel Assault cuz it says the ip while its connecting. If you dont have Tribes, then my best suggestion to find the ps2 ip is while ur ps2 is online, to go to ur computer and either go to the router admin and look at the ip\'s that are listed, or go to ur computer, press run, and type in winipcfg if you have windows 98, and xp is something different, but whichever thing u have to type to see the ip\'s.
Now, if u find ur ps2 ip, go to your router admin, and find somewhere were u can block a certain ip from the router, and if u type in the ps2\'s ip then you will be able to connect to anyone since the router wont be blocking any connections to the ps2 since the router basically doesnt see the ps2.
This was just my case so sorry if this doesnt help. I also have an A-B switch which might be the reason i was able to block my ps2\'s ip.