Internet connection problems

Hi,
I can connect to my ISP and update my virus guard files from the Mcafee tray
icon, but when I try to check my e mail I get a message saying unknown host.
When I try to surf the web I get "Page cannot be displayed." If I ping
www.google.com, from a dos prompt, I just get timed out but if I ping
myself 127.0.0.1 it gives four responses as you would expect. I have
uninstalled internet explorer and then reinstalled it and upgraded it to ver
6.0 but still exactly the same. I did a Windows ME reinstall over my
existing setup but no difference. It all started after someone inserted a
disc to setup BT Connect as the ISP, unfortunately it was a very old disc
and didn't work, just locked up the system.
Has any one any ideas what I can do to remedy my problem.
TIA
Peter