Two lines of black boxes with 16x2 display

Hello!

I'm using a classic display Hitachi HD44780 driver compatible.
I change the RS and the E pin to 7 and 6 and this is my code.

#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 6, 5, 4, 3, 2);

void setup() {
  // set up the LCD's number of columns and rows:
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.print("mind");
}

void loop() {
  
  lcd.setCursor(0, 1);
  
  lcd.print(millis()/1000);

  delay(10);
}

The display returns to me two lines (2x16) of black boxes as arduino doesn't write any to the LCD.

I had checked the solders and the pins with the official tutorial (http://arduino.cc/en/Tutorial/LiquidCrystal) and i didn't find any changes.

Now, i've googled for LCD trouble with black boxes and i saw that the most common issues is one line of black boxes, but nothing about two lines black.

Can anyone help me?
Thank you.16

thecas:
Can anyone help me?

Yes. Adjust your contrast control.