Step 1: turn on The Machine in the power room
Step 2: fill the 5 soul chests around the map (They're the vases). This will open the PaP room.
Step 3: turn on the Voltage Monitor in the PaP room
Step 4: Shoot the 3 red blinking lights (directly under the wall-running TV's). this fixes the brown-out.
Step 5: find 2 wires around the map. (1 in nurses office, 1 in gym locker room)
Step 6: add the wires to The Machine
Step 7: Shoot the machine
You did it! The secret door in the library has now opened.