Ubuntu and D-Link 504T

I already had difficulties last time to have my internet connection work properly with ubuntu, so I expected the same this time, but: the connection this time was there when I used the command line, but did not work when I wanted to start firefox. Well this meant a firmware update of the modem. So I downloaded the new version and there was another file that I downloaded "by chance" - a how to to reset the ADSL-Modem ... well it was one of those feelings: yes, I definitely needed it. I did the whole reset routine so many times and ... well I went to bed frustrated. This morning I tried first with my old windows computer to access the modem, no way - so the last chance was to use ubuntu ... and now: I have a working Internet connection with this ubuntu computer, but no internet connection with my windows computer - for whatever reason :-( I hope that at least by this evening I will have everything more or less running on this computer and then I will care about the other one ... or in the meantime, shutting windows down and reloading it for some strange reason it will work again.