There's a quest in Skyrim where you have to help a witch named Ilia(?) defeat her mother in one of those towers. I got to the top of the tower where there was a hargraven and a hag..and nothing else. After killing them both, I still see the quest icon shown on the grass, and interacting with Ilia produces no response. Was either of the dead characters her mother? The quest remains stuck.
This could be what your looking for. More info would allow for better answers :)
If you go through the stages, go through the door to where the initiation is to start, and a hagraven and a hag in Illia's Mothers place Illia will continue into battle alone killing both of them. If you encounter this Illia's Mother will not appear, not starting the initiation process, she will then return to the top door (If you try to interact with her she will be a blank npc not offering options) ending the quest as unfinished.
PC Note This can be fixed by
prid 0004B47C, enable. Silvia will appear and act hostile but will not initiate combat. Once you attack, Illia will join the fight and the quest will be marked as completed once Silvia is dead.
Taken from uesp.net