Adafruit motor shield apparently interfering with RX input

I am receiving input through the RX pin, but once I add the adafruit motor shield v2 to my arduino uno r3, I no longer see the information in the Serial Monitor.

I used the DCMotorTest example from the motor shield library and added code from the brain library. All my code works if I comment out motor shield code, but uncommenting the motor shield code makes it so that only the motors run and I do not receive any information from the Serial Monitor.

I am not sure why this is happening. The motor shield only uses pins A4 and A5 on the arduino and should not interfere with input from the RX pin.

Any help or insight will be appreciated. I can post my code if necessary.

There are several possibilities here - the first question is what is the source of motor power going to the motor shield? Ideally its complete separate from the Arduino 5V and it must be at least 5V under full load (or the L298 crow-bars the 5V rail)

Got it to work now.

Here’s my new code for reference sake:

/* 
This is a test sketch for the Adafruit assembled Motor Shield for Arduino v2
It won't work with v1.x motor shields! Only for the v2's with built in PWM
control

For use with the Adafruit Motor Shield v2 
---->	http://www.adafruit.com/products/1438
*/

#include <Brain.h>
#include <Wire.h>
#include <Adafruit_MotorShield.h>
#include "utility/Adafruit_PWMServoDriver.h"

// Create the motor shield object with the default I2C address
Adafruit_MotorShield AFMS = Adafruit_MotorShield(); 

// Select which 'port' M1, M2, M3 or M4. In this case, M1
Adafruit_DCMotor *myMotor = AFMS.getMotor(1);

//This is where inserted the arduino brain library
Brain brain(Serial);

void setup() {
  Serial.begin(9600);  // set up Serial library at 9600 bps
  //Serial.println("Adafruit Motorshield v2 - DC Motor test!");

  AFMS.begin();  // create with the default frequency 1.6KHz
  
 
}

void loop() {
  //read input from RX pin
  
  bool motor;
  motor = false;
  
  if ((brain.update()) && (motor == false)) {
  		Serial.println(brain.readErrors());
		//Serial.println(brain.readCSV());
                Serial.println(brain.printDebug());
                Serial.println(brain.signalStrengthOut());
                
                if (brain.signalStrengthOut()==200) {
                motor = true;
                
}
                 
	} else {
        myMotor->run(RELEASE);
}

if (motor == true) {
 int var = 0;
                while(var < 100){
                myMotor->setSpeed(150);
                myMotor->run(FORWARD);
                // turn on motor
               // myMotor->run(RELEASE);
  // do something repetitive 200 times
  var++;
 if (var == 100) {
 motor = false; 
 }
}
}

}




  
/*
 uint8_t i;
  
 //Serial.print("tick");

  myMotor->run(FORWARD);
  for (i=0; i<255; i++) {
    myMotor->setSpeed(i);  
    delay(10);
  }
  for (i=255; i!=0; i--) {
    myMotor->setSpeed(i);  
    delay(10);
  }
  
 // Serial.print("tock");

  myMotor->run(BACKWARD);
  for (i=0; i<255; i++) {
    myMotor->setSpeed(i);  
    delay(10);
  }
  for (i=255; i!=0; i--) {
    myMotor->setSpeed(i);  
    delay(10);
  }

  //Serial.print("tech");
  myMotor->run(RELEASE);
  delay(1000);
}
*/