NPC/Enemy trouble

Hey, guys! New to both this forum and Dark Souls

So anyway, I'm having a problem with my game, maybe it's a glitch, I don't know.
The problem is I can't damage Havel, Kirk, Mildred Maneater, the Prince in Sem's Fortress.. I get numbers above their health bar, but it doesn't move an inch. I was wondering if any of you guys could have any idea as to what is causing this? It's really freaking annoying, and takes away from the experience of the game.

Hoping for some info

How much damage is it showing you do? Is it an issue that you are doing an insignificant amount of damage?

No, it's not that.. Against Kirk I managed to get into a pretty nice combo, and the number it ended on was 1521 damage, more damage than he is supposed to have health. Same thing with Havel and Mildred. I can't seem to do any damage no matter what the number says.

Sounds like a glitch then. Have you tried starting a new character and seeing if you get the same issue?

Otherwise I would say. Quit and reload, see if it happens again.

It happens every time I restart the game, so maybe I need to start a new character.. I can't even damage NPC's if I want to kill them!
I thought maybe it had something to do with me playing in offline mode, but that can't be, right?

Your npc's have modded themselves infinite health? Things are bad on the PC.

This is another really strange bug. I remember hearing that when some people got a hold of Dark Souls early the devs put enemies in with maxed stats and near-infinite health to make things rough on them. Obviously this isn't that, but maybe they were... experimenting with something? I don't know. Weird, man. I was gonna suggest moving forward and returning, but if you've been through Sen's you've already done that.

Yeah, I really messes me up sometimes.. The game is hard enough without me having to run away from Mildred because she doesn't take damage. Really freakin' frustrating