This problem requires you to test both the monitor and the signal input form you cable tv setup. Set the monitor up on a computer and see if it works properly. If it does then you may have a problem with the signal conversion of the cable tv to the monitor. It also could be a weak signal that drops below the monitors sensitivity levels. Have your cable tv repairman check the signal levels on your lines. Another way to test this is to hook up is with a different monitor to test your setup and see if it works. If after testing you find, the monitor does not work properly, then you need to have it serviced. Hope This Helps.