please check this code when i turn on gsm shield led also turn on and keep on and still PIR sensor 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[16];
char n_ref[12];
char msg[1];
char pompe_on[] = "Pompeon";
char pompe_off[] = "Pompeoff";
int swtch=13;
int PIRSensor=2;
int incomingByte;
int val = 0;
void setup()
{
// digit
pinMode(swtch, 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;
}
else Serial.println("\nstatus=IDLE");
if(started){
#ifdef DEBUG_CODE_ON
Serial.println("mise en ligne");
#endif
gsm.SimpleWriteln("AT+CMEE=2");
delay(5000);
#ifdef DEBUG_CODE_ON
Serial.print("AT+CMEE=2");
gsm.WhileSimpleRead();
#endif
//
// PIN CODE
//
#ifdef DEBUG_CODE_ON
Serial.println("PIN CODE");
#endif
//if (gsm.SendATCmdWaitResp("AT+CPIN ?", 1000, 100, "READY", 5) != 1 )
// {
gsm.SimpleWriteln("AT+CPIN=2343");
delay(5000);
#ifdef DEBUG_CODE_ON
Serial.print("AT+CPIN=####");
gsm.WhileSimpleRead();
#endif
// }
//
// INIT FOR SEND SMS
//
gsm.SimpleWriteln("AT+CLIP=1");
delay(500);
#ifdef DEBUG_CODE_ON
Serial.print("AT+CLIP=1");
gsm.WhileSimpleRead();
#endif
gsm.SimpleWriteln("AT+CSCA ?");
delay(5000);
#ifdef DEBUG_CODE_ON
Serial.print("AT+CSCA ?");
gsm.WhileSimpleRead();
#endif
gsm.SimpleWriteln("AT+CMGF=1");
delay(5000);
#ifdef DEBUG_CODE_ON
Serial.print("AT+CMGF=1");
gsm.WhileSimpleRead();
#endif
//
// CMD LOW
//
#ifdef DEBUG_ACTION_ON
Serial.println("INIT PUMP");
#endif
digitalWrite(swtch, LOW);
}
};
void PIRsensor(){
if(digitalRead(PIRSensor)==HIGH){ // read the input pin
digitalWrite(swtch, HIGH); // sets the LED to the button's value
delay(1000);
digitalWrite(swtch, LOW); // delay in milisecond. 3000 = 3 second
}
}
void loop()
{
if(started){
if(digitalRead(PIRSensor)==HIGH){ // read the input pin
digitalWrite(swtch, HIGH); // sets the LED to the button's value
delay(1000);
digitalWrite(swtch, LOW); // delay in milisecond. 3000 = 3 second
}
}
/*
if(started)
{
//
// READ SMS
//
#ifdef DEBUG_ACTION_ON
Serial.println("Wait Read sms");
#endif
if(gsm.readSMS(smsbuffer, 16, n_in, 12))
{
#ifdef DEBUG_ACTION_ON
Serial.println(n_in);
Serial.println(smsbuffer);
#endif
startSMS=true;
//
// filter num gsm
//
/*
if (memcmp(n_in,n_ref,11)==0)
{
#ifdef DEBUG_ACTION_ON
Serial.println("Sender ok");
#endif
// ok
startSMS=true;
}
*/
/*
}
//
// Action
//
if (startSMS){
//
// pump
//
if (memcmp(smsbuffer,pompe_on,7)==0)
{
digitalWrite(swtch, HIGH);
#ifdef DEBUG_ACTION_ON
Serial.println("Pump On");
#endif
}
if (memcmp(smsbuffer,pompe_off,7)==0)
{
digitalWrite(swtch, LOW);
delay (100);
PIRsensor();
#ifdef DEBUG_ACTION_ON
Serial.println("Pump Off");
#endif
}
//
// valve
//
startSMS=false;
// clear SMS
gsm.SimpleWriteln("AT+CMGL=\"REC UNREAD\",0");
}
}
delay(500);
*/
};