Verify the following:

From the System tray, right click the Advanced menu. From the Diagnostics tab, verify that the DNS addresses are green (accessible using PING). If not, contact your service provider. You can Ping a system by entering it's DNS name or IP Address in the field by typing over the name "Network" and clicking the Test button. If you can ping IP Addresses but not names, then your DNS server isn't working. In some cases you may need to change the EnterNet IP Configuration. Click Connections -> Settings -> Advanced button. Change from the default Private API setting to DHCP. Restart the connection.