GPS/GPRS/GSM Shield V3.0 hangs up

HI,

I have an GPS/GPRS/GSM Shield V3.0. And I ran the examples in the wiki page and the program would always hang up after running for sometime. I then try to run a simplified program and the same thing would happen. The following code outputs the raw GPS data from sim908. After a few lines, it just stops. Can anyone help me figure out what is going on?

[code]// Product name: GPS/GPRS/GSM Module V3.0
// # Product SKU : TEL0051
// # Version : 0.1

// # Description:
// # The sketch for driving the gps mode via the Arduino board

// # Steps:
// # 1. Turn the S1 switch to the Prog(right side)
// # 2. Turn the S2 switch to the Arduino side(left side)
// # 3. Take off the GSM/GPS jumper caps from the Uart select
// # 4. Upload the sketch to the Arduino board
// # 5. Turn the S1 switch to the comm(left side)
// # 6. Plug the jumper caps back to GPS side
// # 7. RST the board

// # wiki link- http://www.dfrobot.com/wiki/index.php/GPS/GPRS/GSM_Module_V3.0_(SKU:TEL0051)


void setup()
{
pinMode(3,OUTPUT);//The default digital driver pins for the GSM and GPS mode
pinMode(4,OUTPUT);
pinMode(5,OUTPUT);
digitalWrite(5,HIGH);
delay(1500);
digitalWrite(5,LOW);

digitalWrite(3,LOW);//Enable GSM mode
digitalWrite(4,HIGH);//Disable GPS mode
delay(2000);
Serial.begin(9600);
delay(5000);//GPS ready

Serial.println("AT");
delay(2000);
//turn on GPS power supply
Serial.println("AT+CGPSPWR=1");
delay(1000);
//reset GPS in autonomy mode
Serial.println("AT+CGPSRST=1");
delay(1000);

digitalWrite(4,LOW);//Enable GPS mode
digitalWrite(3,HIGH);//Disable GSM mode
delay(2000);

Serial.println("$GPGGA statement information: ");
}
void loop()
{
while(1)
{
char val;
while(Serial.available())
{
val=Serial.read();
Serial.print(val);

}

delay(1);

}
}[/code]