Depends where you entered the admin room but there is a generator switch that turns off the cameras. Also you can shoot them with your silenced rifle.
Don't have silenced rifle Don't know where generator switch is.
Eventually beat it, but I dunno. Probably was because I didn't explore around much, but I found that really, really difficult. Mainly because the second you get spotted -> alarm -> instant death most of the time. Don't remember MGS being so player-unfriendly before.