@werner I see two different issues here and one is dependent of the other.
So lets start with do you ever get to the FOG iPXE menu? This is the menu where you would pick to register a host or test hardware compatibility?
If no, then what is your dhcp server? Have you configured dhcp options 66 and 67? If yes, what exactly did you enter for dhcp option 66 and 67?
Just load a WIM file, no. That is a microsoft imaging solution.