1. A tile at the lower end of the stair towards the blue key can be lowered.
2. After getting the blue key, head back to the start and follow the arrows.
3. On the way to the exit, press the button on the right wall. Head into the dark area and press the button in the darkness. The computers your passed on your way towards the switch have lowered now.
4. A tile right of the exit switch can be lowered.