If one or more of the thin-film transistors in an LCD monitor are defective, the spot on the screen controlled by those transistors remains dark or a solid color (depending on the design of the monitor) regardless of the signal supplied to it. These dead pixels can appear as small contrasting spots in the middle or edge of an image. A monitor with dead pixels is defective, but some manufacturers don't replace them unless there is more than some minimum number of dead pixels (often six or eight) on the screen. Depending on its location, a dead pixel can either be extremely distracting or easy to ignore.
If there are dead pixels in a new monitor, they usually appear when you turn it on for the first time, so it's important to examine your screen as soon as you receive it. If you discover dead pixels, contact the retailer and explain the problem. Even if you can't return it under warranty as a defective unit, consider sending it back for a refund under the seller's no-questions-asked return policy if they have one.