I am trying this one on Novice and I still can't kill him with the Staff of Magnus. I have even tried using the Console code: setstage mg08 40
I am told to go talk to Tolfir, but Tolfir is too busy because Arcano isn't dead. His health level never seems to even go down. Any suggestions?

If my memory serves me right, you are supposed to use the staff of magnus on the orb to break his magical shield and then attack him.