cant get I2c adapter to work

hello i am in the infancy stages of arduino
i have a mega 2560 and an I2c adpter for my lcd display a 20x4 character
when i load this sketch i get nothing on the display
i had the display hooked up parrallel and it printed the hello world message
since installing this I2c adapter i cant get it to print the message this is the sketch i am using
is there anything missing that would cause this issue

#include <wire.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2c lcd(0x20,20,4);

void setup()
{
lcd.init(); // initialize the lcd

// Print a message to the LCD.
lcd.backlight();
lcd.print("Hello, world!");
}

void loop()
{
}

Are you absolutely sure that the I2C adapter is on 0x20? Have you used Nick Gammon's I2C Scanner to check?

no i am not sure the place i bought it from had a link to that download for the sketch
i will look for that scanning tool you referienced tho thanks for the reply

downloaded the I2c scanner worked great found that the address was 0x27 now that i reloaded the skecth with the correct address things are happening but now i have no backlight anyone be able to shed some light as to what i need to do now
thanks for any help in this

I would start a new topic in the Display section if I were you, the people who frequent that area are very knowledgeable about these things.

Edit: There is already a current topic on this issue. Arduino i2c for 16x2 lcd no backlight or text after upload [solved] - Displays - Arduino Forum

i used this sketchnow it works thanks for all the help and pointing me in the right direction !!!

/* YourDuino.com Example Software Sketch
 20 character 4 line I2C Display
 Backpack Interface labelled "LCM1602 IIC  A0 A1 A2"
 terry@yourduino.com */

/*-----( Import needed libraries )-----*/
#include <Wire.h>  // Comes with Arduino IDE
// Get the LCD I2C Library here: 
// https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads
// Move any other LCD libraries to another folder or delete them
// See Library "Docs" folder for possible commands etc.
#include <LiquidCrystal_I2C.h>

/*-----( Declare Constants )-----*/
//none
/*-----( Declare objects )-----*/
// set the LCD address to 0x27 for a 20 chars 4 line display
// Set the pins on the I2C chip used for LCD connections:
//                    addr, en,rw,rs,d4,d5,d6,d7,bl,blpol
LiquidCrystal_I2C lcd(0x20, 4, 5, 6, 0, 1, 2, 3, 7, NEGATIVE);  // Set the LCD I2C address


/*-----( Declare Variables )-----*/
//none

void setup()   /*----( SETUP: RUNS ONCE )----*/
{
  Serial.begin(9600);  // Used to type in characters

  lcd.begin(20,4);         // initialize the lcd for 20 chars 4 lines

// NOTE: Cursor Position: CHAR, LINE) start at 0  
  lcd.setCursor(3,0); //Start at character 4 on line 0
  lcd.print("Hello, world!");
  delay(1000);
  lcd.setCursor(2,1);
  lcd.print("From YourDuino");
  delay(1000);  
  lcd.setCursor(0,2);
  lcd.print("20 by 4 Line Display");
  lcd.setCursor(0,3);
  delay(2000);   
  lcd.print("http://YourDuino.com");
  delay(8000);
// Wait and then tell user they can start the Serial Monitor and type in characters to
// Display. (Set Serial Monitor option to "No Line Ending")
  lcd.setCursor(0,0); //Start at character 0 on line 0
  lcd.print("Start Serial Monitor");
  lcd.setCursor(0,1);
  lcd.print("Type chars 2 display");   


}/*--(end setup )---*/


void loop()   /*----( LOOP: RUNS CONSTANTLY )----*/
{
  {
    // when characters arrive over the serial port...
    if (Serial.available()) {
      // wait a bit for the entire message to arrive
      delay(100);
      // clear the screen
      lcd.clear();
      // read all the available characters
      while (Serial.available() > 0) {
        // display each character to the LCD
        lcd.write(Serial.read());
      }
    }
  }

}/* --(end main loop )-- */


/* ( THE END ) */ {code}