SIM800L is unresponsive to AT commands

SIMM800L connected to Arduino UNO doesn't respond to AT command. The serial monitor stops at "initializing..."

the LED blinks every 3 seconds VDD --> connected to 5v of the Arduino uno

 #include <SoftwareSerial.h> //Create software serial object to communicate with SIM800L SoftwareSerial mySerial(3, 2); //SIM800L Tx & Rx is connected to Arduino #3 & #2 void setup() { //Begin serial communication with Arduino and Arduino IDE (Serial Monitor) Serial.begin(9600); //Begin serial communication with Arduino and SIM800L mySerial.begin(9600); Serial.println("Initializing..."); delay(1000); mySerial.println("AT"); //Once the handshake test is successful, it will back to OK updateSerial(); mySerial.println("AT+CSQ"); //Signal quality test, value range is 0-31 , 31 is the best updateSerial(); mySerial.println("AT+CCID"); //Read SIM information to confirm whether the SIM is plugged updateSerial(); mySerial.println("AT+CREG?"); //Check whether it has registered in the network updateSerial(); } void loop() { updateSerial(); } void updateSerial() { delay(500); while (Serial.available()) { mySerial.write(Serial.read());//Forward what Serial received to Software Serial Port } while(mySerial.available()) { Serial.write(mySerial.read());//Forward what Software Serial received to Serial Port } }