sim800l keep blinking

i cant receive any message because i think my sim8000l keep blinking every second , what can i do?

what can i do?

Start by posting your program

just like example GSM_Gprs library and i already change tx and rx pin in 50 51 arduino mega

<<
#include "SIM900.h"
#include <SoftwareSerial.h>

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("+6282242790603", "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);
}
};

i already change tx and rx pin in 50 51 arduino mega

But the program does not appear to use them

You #include SoftwareSerial.h but don't appear to use it

You seem to have an object named gsm but I can't see where it is initialised

just like example GSM_Gprs library

Please post the original example code

Where did you get the SIM900.h library from ?

UKHeliBob:
But the program does not appear to use them

You #include SoftwareSerial.h but don't appear to use it

You seem to have an object named gsm but I can't see where it is initialised
Please post the original example code

Where did you get the SIM900.h library from ?

i download at google from searching sim900 library

and no diferrent with original code , i only change my mobile phone number and upload

i download at google from searching sim900 library

That is not really much help

What is the name of the original example that you used ?
Please post the original example code

#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);
}
};

this is the original code what i get from GSM_GRPSLIBRARY_SMS

i already change tx and rx pin in 50 51 arduino mega

What were the pin numbers originally ?
How does the program know about the change of pin numbers ?

UKHeliBob:
What were the pin numbers originally ?
How does the program know about the change of pin numbers ?

yes originally number 2 3 i change it in gsm.cpp with visual studio 2013 from 2 3 to 51 50

yes originally number 2 3 i change it in gsm.cpp

Do you mean that you changed the #DEFINEs in GSM.h and if so, which ones ?