How do I solve "server not found" problems?

I tried the fixes in the links you sent me. They didn't work and without knowing what else to do, I took the computer to the Genius Bar at my nearest Apple store today. Just to remind you, I could not connect to the internet at home using my usual method which is a free dialup. While they didn't fix the computer, they did give me a lot of their time and some further things to try. However, they did find a clue. They were able to connect to the internet on my computer provided it was by ethernet (which I don't have at home as of now) or Airport (which I also can't use at home at this time because I don't have any router at home for the Airport to tap into). At the Apple Store the computer also would not log onto the internet using my wireless extender which I bought as a back up for my dial up (prior to finding out that there was no free wifi within range at home so right now it is just for testing). They could not test dial up because they didn't have a phone jack, but I did test dialup again at another house and again it didn't work. Genius Bar suggested I try the internet in safe mode, if that doesn't work, try reloading to OS and if that doesn't work it may be a hardware issue that I need to take to a third party. In case this is a communication software issue, in the meantime, I want to try reloading the wireless extender software if possible. Does anyone know how to reload the internal modem software? Any other suggestions? Thanks.