I would be happy to try and help you resolve your configuration problems.
I manage to load it Ok but firefox will not load.
How did you install Firefox? Was it with urpmi, or did you download a file directly from Firefox? Konqueror will do most of what Firefox does, it does tend to appear slower than Firefox, but on your system I'm not sure you would even notice the difference.
I read your words on the physical setup. It does not make sense to me. Are you saying this "master computer" is connected to the ADSL modem; and the machien with the problems connects to the mater via an ethernet connection?
In order to help you, we need to understand your setup. If you could better describe this, find out the type of ethernet card, or chip set you have. I also need to know a little about this 'master computer', OS etc.
It appears the adsl modem shuts mandriva down (now she work now she don't)
I hope what ever is going on here will make more sense when we understand the physical connection.
What did you do in Mepis to get it working?