XP and browsing

Has anyone come across XP not being able to browse, even after checking all settings, with ISP etc, change of accounts, pinging, tracert, netstat etc. Even a change of modem, different slots etc, startup programs the works.
You can’t uninstall tcp/ip or even repair or uninstall IE6.
I work as a technician and all of us there have tried everything. We have 2 machines at the moment with the same kind of thing,
Any help would be appreciated as I am getting headaches out of this.
Don’t thing I would go for XP myself.
Thanks Turtle