GPS gives weird characters when powering the ATMEGA328 on and off

i got a problem with my GPS controlled by ATmega328, when i download the code using arduino ISP the GPS works fine and the lcd displays correct data, but when i remove the power from the atmega328 and connect it again the GPS starts to send weird data to the lcd.
the two pictures below illustrates my problem :

      #include "ALCD.H"
      char rowCount;
      char lastPOSy;
      void lcd_reset()
      {
      lcd_port_dir=0XFF;
      lcd_port = 0xFF;
      _delay_ms(20);
      lcd_port = 0x03+LCD_EN;
      lcd_port = 0x03;
      _delay_ms(10);
      lcd_port = 0x03+LCD_EN;
      lcd_port = 0x03;
      _delay_ms(1);
      lcd_port = 0x03+LCD_EN;
      lcd_port = 0x03;
      _delay_ms(1);
      lcd_port = 0x02+LCD_EN;
     lcd_port = 0x02;
     _delay_ms(1);
    }

     void lcd_init (unsigned char rows)
     {
     rowCount=rows;
     lastPOSy=0;
    lcd_reset();         // Call LCD reset
    lcd_cmd(0x28);       // 4-bit mode - 2 line - 5x7 font. 
    lcd_cmd(0x0c);       // Display no cursor - no blink.
    lcd_cmd(0x06);       // Automatic Increment - No Display shift.
    lcd_cmd(0x80);       // Address DDRAM with 0 offset 80h.
     }

   void lcd_cmd (char cmd)
    {
    lcd_port = ((cmd >> 4) & 0x0F)|LCD_EN;
    lcd_port = ((cmd >> 4) & 0x0F);

    lcd_port = (cmd & 0x0F)|LCD_EN;
    lcd_port = (cmd & 0x0F);

    _delay_us(200);
    _delay_us(200);
     }

   void lcd_data (unsigned char dat)
   {
    lcd_port = (((dat >> 4) & 0x0F)|LCD_EN|LCD_RS);
    lcd_port = (((dat >> 4) & 0x0F)|LCD_RS);

    lcd_port = ((dat & 0x0F)|LCD_EN|LCD_RS);
    lcd_port = ((dat & 0x0F)|LCD_RS);

    _delay_us(200);
    _delay_us(200);
    }
    void lcd_gotoxy(char posX,char posY)
 {
 if (posY==0 ) 
    lcd_cmd((1<<7)+0x00+posX);
  else
  {
    lcd_cmd((1<<7)+0x40+posX);
  lastPOSy=1;
   }        
    _delay_us(40);
  }

 void lcd_clear(void)
 {
lcd_cmd(0x01);
_delay_ms(2);
lcd_cmd(0x02);
_delay_ms(2);
}

 void lcd_putchar(unsigned char data)
 {
 lcd_data(data);
 }

void lcd_puts( char *str)
{
unsigned char i=0;

while(*(str+i)!='\0'&&i<rowCount)
{
lcd_data(str[i]);
i++;    
}
if (i>rowCount-1&&lastPOSy==0)
{
    i=rowCount;
    lcd_gotoxy(0,1);

while(*(str+i)!='\0')
{
lcd_data(str[i]);
i++;    
}
}

}

void lcd_putconsts(const char *str)
{
unsigned char i=0;

while(*(str+i)!='\0'&&i<rowCount)
{
lcd_data(str[i]);
i++;    
}
if (i>rowCount-1&&lastPOSy==0)
{
    i=rowCount;
    lcd_gotoxy(0,1);

while(*(str+i)!='\0')
{
lcd_data(str[i]);
i++;    
}
}
}