since nothing else has worked, try this
http://www.hostmysite.com/support/info/flushdns/
that should work, unless your firewall is doing something very funky, or you have a virus/adware/spyware/malware/conflicter (did you install any antivirus programs such as Vista Anti virus, or windows anti virus, or something similar, that is a virus that my gf and her sister has gotted 2ce each, the silly girls, but one of the common symtoms are that certain websites become inacessable for no reason)(yes it's a virus pretending to be anti virus software)
if that doesn't work, try acessing it trough a proxy like the following
http://www.sitesurf.net/surf.php?q=Z...vbQ%3D%3D&hl=0