Your FOG Server needs to remain running. It’s the server providing PXE for your clients.
When you installed, did you setup your fog server as the DHCP server?
Is your setup now within your local network? Or did you setup with your public IP Address?
PXE works by linking to the system, so if you’re using Public IP address, it’s being stopped by your router as chances are it’s trying, essentially, to make a loop back to itself which the router typically will not allow. If not, are you sure firewall is not running? You can stop the firewall in Fedora 19 with the commands:
service firewalld stop; chkconfig firewalld off
You understand that PXE only works from the Network Adapter via Cable as well? You’re not attempting to PXE boot over wireless correct?
Again, more information about your specific setup. We can’t help if we don’t have the information.