Arduino Micro: Followed the BlinkWithoutDelay instructions, but somehow it's not working in my code

Question

Any help would be greatly appreciated!

/*
   Jebediah's Launch Control System for Kerbal Space Program
   Alpha Build 2.00
   An Open-Source Project by John Seong
*/
#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <Keypad.h>
const byte ROWS = 4;
const byte COLS = 3;
const int buzzer = A3;
const int ledAbort = 5;
const int ledStage = A5;
const int buttonAbort = 4;
const int buttonStage = A4;
int ledAbortState = LOW;
int ledStageState = LOW;
char keys[ROWS][COLS] = {
  {'1', '2', '3'},
  {'4', '5', '6'},
  {'7', '8', '9'},
  {'*', '0', '#'}
};
byte rowPins[ROWS] = {12, 11, 10, 9};
byte colPins[COLS] = {8, 7, 6};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
LiquidCrystal_I2C lcd(0x3F, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
unsigned long previousMillis = 0;
const long interval = 1000;
// Show a two-line message on the LCD.
void lcdShow(const char line0, const char line1) {
  lcd.clear();
  lcd.print(line0);
  lcd.setCursor(0, 1);
  lcd.print(line1);
}
void lcdShowResult(float result) {
  lcd.print(result);
}
void setup() {
  pinMode(buzzer, OUTPUT);
pinMode(ledAbort, OUTPUT);
  pinMode(ledStage, OUTPUT);
pinMode(buttonAbort, INPUT_PULLUP);
  pinMode(buttonStage, INPUT_PULLUP);
pinMode(buzzer, OUTPUT);
  Serial.begin(9600);
  lcd.begin(16, 2);
  lcdShow("  JEB'S LAUNCH", " CONTROL SYSTEM");
  delay(3000);
  lcdShow("ALPHA BUILD 2.00", " STUDIO HORIZON");
  delay(3000);
  lcdShow("WELCOME, KERMAN.", "PRESS ANY KEY...");
  while (!keypad.getKey()) ;  // wait for key press
}
void loop() {
  static enum {START, MENU, SET_COUNT, COUNT_DOWN, LAUNCH, SET_THRUST, SET_WEIGHT, TWR_COMPUTE} state = START;
  static uint32_t last_second;  // millis() value on last full second
  static int count;
  static float thrust, weight, ratio;
char key = keypad.getKey();
switch (state) {
    case START:  // transitional state
      lcdShow("1. LAUNCH SEQ", "2. TWR CALC");
      state = MENU;
    /* fallthrough */
case MENU:
  if (key == '1') {  // Countdown
    lcdShow(&quot;COUNTDOWN TIMER&quot;, &quot;SECONDS: &quot;);
    count = 0;
    state = SET_COUNT;
  } else if (key == '2') {  // TWR
    lcdShow(&quot;TWR CALCULATOR&quot;, &quot;THRUST: &quot;);
    thrust = 0, weight = 0, ratio = 0;
    state = SET_THRUST;
  }
  break;

case SET_COUNT:
  if (key &gt;= '0' &amp;&amp; key &lt;= '9' &amp;&amp; count &lt;= 99) {
    lcd.print(key);
    count = 10 * count + (key - '0');
  } else if (key == '#') {
    lcdShow(&quot;    T-MINUS&quot;, &quot;     SECONDS&quot;);
    // Force a refresh on entering COUNT_DOWN:
    last_second = millis() - 1000;
    count++;
    state = COUNT_DOWN;
  } else if (key == '*') {
    state = START;
  }
  break;

case COUNT_DOWN:
  if (millis() - last_second &gt;= 1000) {
    last_second += 1000;
    count--;
    if (count &lt;= 10) {
      tone(buzzer, 500);
      delay(500);
      noTone(buzzer);
    }
    if (count == 0) {
      Serial.println(&quot;Lift off!&quot;);
    } else if (count &lt; 0) {
      state = LAUNCH;
      break;
    }
    lcd.setCursor(1, 1);
    lcd.print(count &lt; 10 ? &quot;  &quot; : count &lt; 100 ? &quot; &quot; : &quot;&quot;); // pad
    lcd.print(count);
  } else if (key == '*') {
    state = START;
  }
  break;

case LAUNCH:
  tone(buzzer, 3000);

  int stageConfirm = digitalRead(buttonStage);
  int abortConfirm = digitalRead(buttonAbort);

  unsigned long currentMillis = millis;

  if (currentMillis - previousMillis &gt;= interval) {
    previousMillis = currentMillis;

    if (ledAbortState == LOW) {
      ledAbortState = HIGH;
      lcdShow(&quot; T-ZERO WARNING&quot;, &quot;CONFIRM IGNITION&quot;);
    } else if (ledAbortState == HIGH) {
      ledAbortState = LOW;
      lcd.clear();
    }

    if (ledStageState == LOW) {
      ledAbortState = HIGH;
    } else if (ledAbortState == HIGH) {
      ledAbortState = LOW;
    }
    digitalWrite(ledAbort, ledAbortState);
    digitalWrite(ledStage, ledStageState);
  }
  break;

case SET_THRUST:
  if (key &gt;= '0' &amp;&amp; key &lt;= '9' &amp;&amp; thrust &lt;= 9999) {
    lcd.print(key);
    thrust = 10 * thrust + (key - '0');
  } else if (key == '#') {
    lcdShow(&quot;TWR CALCULATOR&quot;, &quot;WEIGHT: &quot;);
    state = SET_WEIGHT;
  } else if (key == '*') {
    state = START;
  }
  break;

case SET_WEIGHT:
  if (key &gt;= '0' &amp;&amp; key &lt;= '9' &amp;&amp; weight &lt;= 9999) {
    lcd.print(key);
    weight = 10 * weight + (key - '0');
  } else if (key == '#') {
    lcdShow(&quot;THRUST-TO-WEIGHT&quot;, &quot;RATIO: &quot;);
    if (thrust != 0 || weight != 0) {
      ratio = thrust / weight;
      lcdShowResult(ratio);
    }
  } else if (key == '*') {
    state = START;
  }
  break;

}
}