That flickering flash (I think) actually tries to help your auto focus get enough light to automatically focus. But sometimes the surroundings are so dark, not even that flashing light is enough to allow the auto focus to find the necessary reference points for focusing. So the camera will just NOT fire. If that is the case, and if in that case you CAN, switch on more light.
By the way, if there are people in the room, some may be increasingly irritated by that flashing pre-flash (I would), so don't try it too often with people in the picture (I say, from my personal point of view ).