Trying to contact your webserver with it's public ip through some routers is pretty much impossible. Your router sees an http request comming from a local pc (on it's private network) and automatically serves up the router config pages. Even if you have port forwarding enabled, the router still doesn't see this as incomming traffic so it doesn't forward it.
There is an answer, though.
When an external request is made for
www.yourdomain.com, it resolves to it's public ip which leads straight to your router. Your router (if configured properly) will then forward the request to your designated webserver and
www.yourdomain.com will now resolve to the private ip of your server.
You can resolve
www.yourdomain.com internally by adding it to your hosts file:
'C:/windows/system32/drivers/etc/hosts'
Load this file into notepad and you'll see that there's already an entry there for 'localhost'. Simply add an entry for
www.yourdomain.com with your server's private ip. You can now access your site normally without your router messing you about.
You can check that your public dns resolves properly by using a proxy (google it) but other than that (and download speed), it's just like public access.
Of course, this is just one link in a chain of settings that need to be correct.