A method and a display device for detecting an abnormal video signal by periodically checking R,G,B signals. The method includes selecting an R,G,B signal and setting a region of the selected signals to be checked; detecting a minimum pixel level value in the region of the selected R,G,B signal; comparing the minimum pixel level value for the selected R,G,B signal with a predetermined threshold value and checking if abnormal R,G,B signal are present; and displaying on a screen a message indicating whether the selected R,G,B signal is abnormal.