LCD not displaying any character with I2C or when used separately

Question

I have an arduino uno and pin connection for I2C are -

SDA --> A4
SCL --> A5 
VCC --> 5v
GND --> GND

This the code i am uploading taken from the examples -

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

// Set the LCD address to 0x27 for a 16 chars and 2 line display
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup()
{
    // initialize the LCD
    lcd.begin();

    // Turn on the blacklight and print a message.
    lcd.backlight();
    lcd.print("Hello, world!");
}

void loop()
{
    // Do nothing here...
}

The LCD shows nothing after upload . I have tried adjusting the potentiometer on I2C; just the blank characters come up.