There is a door to the right of the arcade, and the lever to restore power to the infirmary should be right there after walking through said door. Note, you have to walk through the entrance to the arcade section and look right. It's a little hard to explain but I hope you can find it. If not, start trying random doors. The game is pretty fairly streamlined in that you won't be able to go much anywhere else than where you need to at that stage