Does your /etc/hosts and /etc/resolv.conf configuration files show the correct info for your isp/network?
My /etc/hosts file:
# Duron 850 tinwhistle /etc/hosts file
# Do not remove the following line, or various programs
# that require network functionality will fail.
127.0.0.1 tinwhistle localhost localhost.localdomain
And my /etc/resolv.conf file: