You've done a good job describing your problem. This could be a DNS server
issue
This page has some good troubleshooting steps which may help identify what the problem
is. You may need to contact your IP about the issue. They'd be able to help.
http://www.duxcw.com/dcforum/DCForumID1/224.html
I've had similar problems with my DSL service. They gave me some other DNS servers
to use, rather than obtain DNS server automatically.
Blocking Unwanted Parasites with a Hosts File