If you already have the lighter and you have returned to the starting room, than there is nothing else to do but to light the candle . If it is burning, and you still cannot see any ghosts, then walk up to the clock  and use it to switch time to 4 pm. A ghost should then appear . Talk to him, until all of the dialog options have been exhausted. This way, you will learn about the existence of a secret switch, which is essential to completing the task.
Now return to the chamber in which you have found the lighter. Use the door indicated in the picture above.
Approach the wardrobe and interact with it. This way, you will activate the secret switch, which the ghost has mentioned. After that, return to the starting room following a safe path.