Dungeons: In hufflepuff's common room, there aren't any active threads anymore. All are dead. Guess all of them (besides "Hufflepuff Notice Board" and "Quiddtich Tryouts!") can be deleted.
As for the kitchens (no moderators are there so I thought that I should mention it), there are three unactive threads.
Third floor: There are no things that are necessary to delete. Although, there are two ended threads.
"
Basic class 1st" and "
NEWT class 1st".
No threads in the gallery.
Fourth floor: In library, there are all threads dead. However, there is Naomi Quinn-Greyback's topic, which is open, and Angelique Pyrites replied to it few days ago. So i think you can leave it there, and we'll see if the Angelique will come back to reply.
In Empty classroom, there are 5 dead threads and one thread Open and awaits for Lucy Weasley's reply. The thread was also made by her, and the last post was made on November the 3rd.
Staff room - Both of the threads over there are dead. It also seems that the thread which was made by Caelani Bittel won't be active anymore.
And under the forum Fourth floor itself is a thread, made by Marki Gordon, and it's awaiting for it's reply from Walker Marshall.
{***}
So that's all from me