You have two kidneys, each about the size of a fist, located on either side of the spine at the bottom of the rib cage. Each kidney contains about one million functioning units called nephrons. A nephron consists of a filtering unit of tiny blood vessels, called a glomerulus, which is attached to a tubule. When blood enters the glomerulus, it is filtered and the remaining fluid then passes through the tubule.
In the first case, each time the computer starts up, the question mark appears and flashes for a few seconds, then disappears. The cause of this symptom is that there is no hard drive selected in the Startup control panel. Remember that selected on the Macintosh means that an icon is darker than the other.
What Are Flashing Lights? When flashing lights occur you may think that you see lights going on and off, especially to one side. These tend to happen in only one eye at a time, even when your eye is closed. What Causes Flashing Lights? The vitreous sometimes pulls on the retina. This may cause you to see flashing lights or lightning streaks, even though there aren't any such lights present. This is the same thing that occurs when you get hit in the eye and see stars or when you rub your eye.