You see the radiation hazard symbol and the words, "Reactor one status: Offline."
There are a few options for what you can do, but your security clearance doesn't seem to be high enough to activate the reactor from here. You can: access the intercom, send a message to the control room's terminal, view the reactor's status, make a video-call to the control room, or open the door. You suddenly remember that only Reactor Technicians are cleared to make adjustments to the reactors, including turning them on or off. If you could find a reactor technician's security card, all you'd have to do then was push the "on" button.
It seems that this place was abandoned in a hurry, maybe some reactor tech left his card laying around somewhere?
As a side note, it looks like any room with a mechanical door can be opened remotely using this system, as long as you would have clearance to open it anyway.