Yes I know I am a fucking dumbass and I should've probably tested it in vmware and so forth.

Long story short is, I replaced my authui.dll with a modified one to regain my former glory in forms of customization.
Now I can't get past my login screen due to it being pitchblack.

So I can't enter my password, nor get inside to undo the damage I've done.

Is there some way I can possibly get in to a CMD before booting windows?
I know how to undo the damage but I can't without access to explorer or cmd.

I've tried launching it in failsafe and all that.
Note: I don't have a CD and I don't own a big enough memory stick to launch the system repair disk and go that way.

And I've read somewhere about advance boot options but I can't seem to get in to it.

Any help?