Assuming your A-records for your domain are pointing at your ip and you have made the right port forwarding settings on your router, the problem must be in the setup of the httpd.conf. Maybe Izzy can tell how Apache grabs the request headers for your web site, but it should be pretty straightforward.
I bet you tried
http://<global-ip>/, so what I would do is to get a remote portscan from a site like
http://grc.com they have a service called shields up and see if the port you are using to serve your web pages are open, that is if you dont use port 80.
You need to supply more information for the community to troubleshoot your problem
Alslo check your dns records with nslookup might give you a clue to where the problem is