PIR sensor and gsm shield problem???

when i put code like this when i turn on my gsm shield PIR sensor is not working.

#include "SIM900.h"
#include <SoftwareSerial.h>
#include "sms.h"
#include "gsm.h"
#include "string.h"
#define DEBUG_CODE_ON
#define DEBUG_ACTION_ON
SMSGSM sms;
boolean started=false;
boolean startSMS=false;
char smsbuffer[8];
char n_in[8];
char pompe_on[] = "Pompeon";
char pompe_off[] = "Pompeoff";
int led=13;
int PIRSensor=2;
void setup() 
{  
  // digit
  pinMode(led, OUTPUT);
 pinMode(PIRSensor, INPUT);
  //Serial connection.
  Serial.begin(9600);  
  Serial.println("GSM Shield testing.");
  // GSM START
  if (gsm.begin(9600))
  {
    Serial.println("\nstatus=READY");
    started=true;  
  }
}
void loop() 
{ 

  if(started){
    if(digitalRead(PIRSensor)==HIGH){   // read the input pin
      digitalWrite(led, HIGH);      // sets the LED to the button's value
      delay(1000);    
      digitalWrite(led, LOW);   // delay in milisecond. 3000 = 3 second
    }
 
  }
}

but when i put this code like this then if gsm shield is off PIR sensor is working but not working when gsm shield is on

void loop() 
{ 
   if(digitalRead(PIRSensor)==HIGH){   // read the input pin
      digitalWrite(led, HIGH);      // sets the LED to the button's value
      delay(1000);    
      digitalWrite(led, LOW);   // delay in milisecond. 3000 = 3 second
    }

  if(started){
 
 
  }

}