LiquidCrystal_I2C blank up after unplug usb cable

Recently im testing on I2C/TWI LCD 1602 for my assignment. Everything go fine except when i unplug usb cable from computer and using power adaptor. The lcd screen will blank up when i unpluy the usb cable and resume when i plub in the usb cable again. Any thing wrong with the library? I testing with the code below:

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

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

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

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

void loop()
{
}

Any thing wrong with the library?

How would we be able to tell without a link to the library?

It seems to be a power supply problem so a diagram or a photograph would help.

Don