Have you checked to see if you're not a continuing victim of the DNS worm that was going around?! The FBI just recently stopped DNS changer services on July 9, 2012 so hopefully that's not the reason. (For more, here's a link to read: http://digitalsaliva.com/internet-shutdown-9july-dns-changer/ )
If you're sure that's not the reason then you might want to adjust your router and browser's DNS service to someone like OpenDNS (http://www.opendns.com/) assuming you're on your own account and not in a dorm setting or connected to free WiFi or something.
But most of all you may want to check your browsers settings. For example, you may want to adjust your browsers ability to resolve web addresses using a web service, predicting network actions, or using a prediction service and disable them. These are advanced settings in Chrome just in case you're wondering. But there are similar settings like that in most of the other major browsers too. These things may be more convenient but they are not without risk. So I suggest turning them off.