I have a problem where nothing spawns after the goat.. The portal appears but nothing comes out of it. This is my second playthrough on PC with mods. Don't know what mod could be effecting it.
Turn all the mods off do the quest then turn them back on, or check the pages and comments back at Nexus or Steam Workshop wherever you got your mods from for any conflicts to see which might be causing the lack of goat.
Like the quest pages walkthough says ignore the atronachs and fire at the two men (the guards with helmet).