SIM808 - GSM/GPRS - ARDUINO - DB:NO RESP

Hi, i was using the sim808 with arduino. I connected the sim’s tx in arduino’s digital (7) and the rx in digital[8].
Yesterday was working, today i’m trying again, in a new pc and new arduino, but the same sim808, and when i start the “gsm.begin(2400)” the only answer is DB:NO RESP. And its so weird cause yester are working 100%. I changed the GSM.cpp for my serial ports, i have no idea from what is happening.

#define _GSM_TXPIN_ 7
#define _GSM_RXPIN_ 8

Im waiting for yours help. Thanks from now. I will paste the code here:

#include "SIM900.h"
#include <SoftwareSerial.h>
//If not used, is better to exclude the HTTP library,
//for RAM saving.
//If your sketch reboots itself proprably you have finished,
//your memory available.
//#include "inetGSM.h"

//If you want to use the Arduino functions to manage SMS, uncomment the lines below.
#include "sms.h"
SMSGSM sms;

//To change pins for Software Serial, use the two lines in GSM.cpp.

//GSM Shield for Arduino
//www.open-electronics.org
//this code is based on the example of Arduino Labs.

//Simple sketch to send and receive SMS.

int numdata;
boolean started=false;
char smsbuffer[160];
char n[20];

void setup() 
{
  //Serial connection.
  Serial.begin(9600);
  Serial.println("GSM Shield testing.");
  //Start configuration of shield with baudrate.
  //For http uses is raccomanded to use 4800 or slower.
  if (gsm.begin(2400)){
    Serial.println("\nstatus=READY");
    started=true;  
  }
  else Serial.println("\nstatus=IDLE");
  
  if(started){
    //Enable this two lines if you want to send an SMS.
    //if (sms.SendSMS("3471234567", "Arduino SMS"))
      //Serial.println("\nSMS sent OK");
  }

};

void loop() 
{
  if(started){
    //Read if there are messages on SIM card and print them.
    if(gsm.readSMS(smsbuffer, 160, n, 20))
    {
      Serial.println(n);
      Serial.println(smsbuffer);
    }
    delay(1000);
  }
};

Go back to basics. Load the Arduino with a simple 'serial relay' program and see if you can get the 808 to respond to basic AT commands.