I suggest you try
. This should switch off your firewall. Just to check if it is the firewall that is the problem. (Switch it back on afterwards off course, I am not suggesting you run with out a firewall)
Another thing. Try to not use vncpasswd and see what happens. Even if it says a password will be required. You will be prompted for a password when you login from your Windows machine. This password should be the same as the one for the user to whom that specific vncserver process belongs, ie the user that started the vncserver. Just enter it at the time you run vncviewer. Not sure if this will sort your problem out, but it might just.