possible reasons and solutions:

1. no AC power input:  make sure the power supply works well;

2. connection between sending card and LED screen is not good:  check the cable connecting them;

3. the devices such as function-card between sending card and LED screen fail: check the devices;

4. no DC 5V power for the first receiving card or the first receiving card is out of work: check the power or the replace the receiving card;