First, be sure that you have the enamel plate from Dracula's bedroom.
This from UHS Hints:
At the top of
the (library) ladder, you should see a crank.
Turn the crank to move the ladder.
There is something interesting on the wall behind the books.
It appears to be a light of
There is something in the library that needs to be fixed first.
It is somewhere nearby, on the bookshelves.
Starting with your back to the door (where you entered from the balcony), move forward two times.
Turn to the shelves on your right.
Look for an oval-shaped opening on the shelves.
It is at the fourth set of
shelves from the corner, between the third and fourth shelf of
Use the enamel plate with the eye.
Go back to the ladder. Turn on the light