It could be a proxy problem.
Have you tried specifying a proxy in your browser, on either computer?
See:
http://www.cableforum.co.uk/board/article.php?a=21 for how, &
http://www.cableforum.co.uk/board/article.php?a=10 for a list of proxies.
Are the browser connection settings different on the two PCs? Perhaps one has a proxy specified & one does not?