Do you know what a dead pixel is? Over time, some pixels in your monitor can stop working correctly. You can find them because they always shine in your monitor, or are black, but can't be modified because they're dead.
This Undead Pixel program lets you detect exactly which are the dead pixels, and in LCD monitors can repair some of them (not all can be repaired). The way of fixing them is to expose them to very quick and continuous changes over a period of time. Not all respond, but some do, and start working again. To do this you need to run Undead Pixel for a couple of hours.
NOTE: For Undead Pixel to work correctly you ned to install Microsoft .NET Framework in your PC.