Serial.begin messes up my 74HC595 Shifter

I am doing a school project that involves lots of Outputs. I need to use one 7segment display so i decided to use shift register. Register works fine until the point i type Serial.begin under my setup(){}. The whole 7 segment goes crazy and random lights starts when booting program. Sometimes all segments are on.

As soon as i remove the Serial.begin line everything works. What to do? Shifter uses same serials that i try to use or what what is happening? I am using Arduino Uno. Thank you. My main is like this:

#include "Display.h"

void setup()
{
 pinMode(0, OUTPUT); // ClockPin
 pinMode(1, OUTPUT); // LatchPin
 pinMode(2, OUTPUT); // DataPin
}

void loop()
{ 
 Ykkonen();
}

And my Display.h follows

#include "Arduino.h"

void Ykkonen()
{
  int ClockPin = 0;
  int LatchPin = 1;
  int DataPin = 2;
  
  digitalWrite(LatchPin, LOW);
  shiftOut(DataPin, ClockPin, LSBFIRST, B10001001);
  digitalWrite(LatchPin, HIGH); 
}

int ClockPin = 0; int LatchPin = 1;

These are the Serial lines. Use other pins.