Your probably looking at a bad display or a bad video cable.
If this is a desktop computer and you have another computer around to swap displays, does the problem also happen with the other display?
If problem goes away then you know its not the computer.
If problem goes away with different monitor then swap video cables between them, VGA, DVI or HDMI etc. If the problem comes back using the cable from the troubled display or goes away using the cable from the good display on the monitor that was acting up, then you just need to replace the cable. If the problem remains on the troubled display no matter of cable swap then your likely looking at buying a new monitor to replace this one.
*If this is a laptop computer, your most likely looking at having to replace the display, however a good test would be to plug a monitor to the VGA out or HDMI out port on laptop and test to make sure its not the GPU that is causing this. If the problem is not observed on another display plugged into video output of laptop then its just the internel display is bad or ribbon cable between the laptop display and the main board has a break in it. Some ribbons can be replaced while others are soldered to the display and come as one assembly. The ribbon cable on the laptop flexes every time the laptop is opened and shut so this can lead to cable failure. Sometimes the break is a fracture and the display can be closed part way or opened further to get all the colors back etc to show that there is a connection issue with the cable.
