After Playing Itunes on a remote computer and including Apple TV as a set of speakers, I could no longer access ATV. When I reboot, I see the animation and then after that just a black screen. I ran the Apple TV diagnostic and it says there is a network problem. I disconnected the 2T external drive, because the same thing used to happen if the drive got powered off. I see no way to access the menus to check network. Should i just do a Factory Reset and start over? I hope not. But unless someone comes up with a fix pretty quick I may have to… 
Thanks
Is your external drive being used for primary (iTunes syncing) storage? If so, it will need to remain connected at all times, including when the AppleTV starts up.
I'm having similar problems - after a restart I get the opening aTV screen then a black screen. I have a external drive as my primary storage and it is connected. If I do a factory reset what steps do I take to prevent a loss of content on the drive?
By chance, has your AppleTV system software been updated recently?
P.S. Fixed your post :)