Explore the Theatre
Quickly go into the bathroom to find some Supplements, then go up to the next floor. Here you'll want to head left to find an Artefact on the table, then go to the end of the corridor to find a Trading Card.
Turn on the power
Next up you'll want to head through the white door, then go into the Projection Room to find an Artefact near the laptop, now go outside and climb up to the roof. Activate the generator, then return to the Projection room and interact with the radio to find some keys.
Finally, go downstairs and open the locked door with the keys, then walk down to the stage to find an Artefact on the box, now open the curtain to view a cutscene.