There are three brooms in the game:
- One in the white (art) room
- One in the lift room in the dark
- One in the miscellaneous interaction room next to the door you enter the room
Make sure they are all turned knocked over, and the achievement should be unlocked.
Some people have reported problems with the achievements if they have taken screenshots or brought up the Steam overlay. To be safe, start a new game from the desktop and play through for the achievements.