.. a member gives us such little information about their problem.. No mention of router make or model, no mention of the computer operating systems in question.. Are all the connections wired or are all wirelessly connected? The EXACT error was not listed, nor did you indicate your ISP. Have you contacted your ISP about the issue? Do you have all the same security software on ALL of the computers? Using Norton? If so, uninstall and see if it fixes the issue.
Still, since I've tried connecting to the website you've listed on three different machines, using two different broadband connections, and the site comes up easily, I would start eliminating parts of the equation.. Remove the router and connect directly to the modem.. Does it still not connect? If so, try resetting the modem again.
Are any of the computers laptops with wireless connections? If so, can you connect to the site using a different network at a friend or family member's house?
Hope this helps and let us know more.