Okay so, I've gotten to the point where I turn in the lexicon and to septimus and now he wants me to collect blood. I know Im supposed to have a conversation with Hermius Mora and the Wretched Abyss shows up, things are going good BUT I cant interect with it no matter how many times I press the E button to activate dialoge. I've tried everything I can think of to prompt a reaction reloading, waiting, aggroing Septimus and sheathing my weapons but nada. I've looked around but there doesnt seem to be much info on the issue so I figured I'd come here in the hopes of finding a fix because as it is my only options seem to be kill Septimus and fail the quest or keep it in my log indefinatly.

I'm not running any mods, I do have all the current DLC I dont have any of it loaded so the games running pretty much vanilla.

Can you reload a previous save? Maybe advance the quest with console commands?

Load a save made prior to entering Septimus's cave. If that doesn't work, you might need to activate the Dragonborn DLC and try again.

Back away from Hermae-Mora, sometimes I have had to activate Him while on the ramp.

Yeah; you run up the little ramp and Herma Mora gets you right at the top.
He fills up the hallway and I think it 'grabs' you - can't remember.
Do you get 'grabbed'?

Does anyone remember for sure?
Or does he just fill up the hallway so you bump into him (the hallway's blocked)...?
I seem to remember it's automatic. You shouldn't need to initiate dialog with him.
I just did this a coupla weeks ago but my memory svcks lately.

What is your platform, PC?
You should be using all the Unofficial patches.
This is the type of thing they fix... because I remember this was a known bug on the forums, back when the game was new.