Do you still have the Orange software on the machine? That usually installs a proxy server on the PC and can cause DNS resolution headaches, especially with a router (not so bad with the old ADSL modems)
Take a look in your internet connection settings and disable any proxy, or any DNS settings which point to Orange
Personally I prefer to use the OpenDNS servers at 208.67.222.222. and 208.67.220.220
If you want to make your network kiddy-safe, try using their servers at 208.67.222.123 and 208.67.220.123