Forget the web forwarding for the moment, and make sure the webserver has Internet connectivity. Make sure you web browse to the Internet.
Once you know that works, take a look at Windows firewall (and any software firewall). If you have moved the subnet it is in, Windows might have changed to blocking all inward ports again.
Once you know those two are good, come back to the inbound forwarding. Can the MX ping the web server ok (to verify network connectivity)?