So I've taken the blood back to Septimus and he's opened the thingy. I've followed him through and can see the book on a stand. He doesn't get fried and if I try to talk to him it just says This Person Is Busy. I can't get or read the book either. I'm at level 40.

Any ideas what I might have done wrong and what I can do to progress?

Reload a previous save. These things should be fairly obvious.