Can't remember the code, finished the game awhile ago. But go to the old woman from the net of the mask? guild. She'll say something with numbers. That is the sequence of the books in the library you need to activate.
If you can post screenshots or write down what she says I can help out. Because I don't have a savegame at that point of the game :P Or perhaps an other member can help you out.
"he who read no books reads the first book. he who reads the first book reads the fourth book, he who reads the fourth book reads the third book, he who reads the third book takes a peek at the first book"