A liquid crystal display includes a system and a liquid crystal module. The system detects an input frame frequency, generates a DISP signal indicating the input of an abnormal signal at a high logic level when the detected frame frequency is within a previously determined range, and generates the DISP signal at a low logic level when the detected frame frequency is beyond the previously determined range. The liquid crystal module includes a signal processing unit which selectively outputs digital video data for implementing a normal screen and digital black data for implementing a black screen in response to the DISP signal.