Is your target computer, fog server and dhcp server on the same subnet? If yes, then I think the best test is to use tcpdump to capture the pxe booting process to see what the dhcp server is really telling the client.: https://forums.fogproject.org/topic/9673/when-dhcp-pxe-booting-process-goes-bad-and-you-have-no-clue
You can review it with wireshark or upload the pcap to a google drive and post the link here. If you don’t want to post the link on a public forum you can IM me and I will take a look to see what is going down the network.