Well you've eliminated your OS, your laptop, and the connection to the Internet. That leaves firewall and DNS. It's not likely that the firewall got set for one website without your knowledge, so I would look at a DNS problem. And easy way to test that is to switch to a more reliable DNS server.
I use OpenDNS. It's free and less vulnerable than ISP servers.
www.opendns.com/
You should be able to set it in your router.