If you are running any spyware/adware, anti virus, firewall etc then turn them all off and try again - if it works then one of them is blocking the site. Also turn off any search bars you may have installed on your web browser too.
Have you tried disconnecting from the web and then reconnecting?
Also - sometimes this happens in IE where you cant type in a link in the address bar (beats me why) so go to google.com - type in the URL and then click the result which should be the direct link to the site - that way you are linking to it and not using the address bar to type it in.
Cheers
Maz
