The network light and power light could be a good basis for judgment.
a) If the power light is on and the network light is flashing: the SIM card is not ready, which means that the SIM card will not work after electrostatic discharge. Please check the SIM card and improve the anti-interference ability.
b) If the power light is on, and the network light is on or normally on: The module is blocked, which is due to poor performance of the customer's PCB. If the power supply and GND loops are normal, please check the GND state, and if the surge protection is good, please check …. It is recommended to connect the TVS on the RESET pin of the module to GND.
c) If the power light is off: The module has surely been powered off, which is caused by the customer's power supply. Please improve the anti-interference ability of the power supply.