First of all, Try the site with
www.hidmyass.com - If it works with it - As someone said : It's Your Firewall.
Maybe you got some spywarisch program which changed you're 'host-file'.
Go to C:\Windows\System32\Drivers\etc and then you'll see a file called 'host' with no extension. Now open it in notepad and paste it here in a [/code]