Arduino Reaction LED game
Your are not explicitly initializing the variable isChanging, so the compiler sets it to 0. This means, that your code will directly go to the last else statement and cannot at any time reach the LED code, because you are not changing the variable in the else statement.

But I don't really understand, why you were using this variable in the first place. Try to use purely non-blocking code. For checking the button you can do something like this:

boolean button_pressed = false;
unsigned long button_timestamp = 0;

void loop(){
  ...
  if(!button_pressed &amp;&amp; digitalRead(11)){
    button_pressed = true;
    button_timestamp = millis();
  }
  if(button_pressed &amp;&amp; millis() - button_timestamp &gt; 50){
    if(digitalRead(11)){ // real button press
      button_pressed = false;
      // check, if the middle LED is ON and act accordingly
      // or, if the game hasn't started yet, start it
    } else { // just a bounce of the button, not a real button press
      button_pressed = false;
    }
  }

  // LED CODE
  if (millis() - lastChange &gt; 500) {
    ...
  }
}


Note, that this code will not wait for the button to be released, but reacting, when the button was held down for 50ms. You can change this value, to a one, that is more fitting your used button, but it is a good start point.

Also in your LED code, you have to replace the 500 in the millis statement with a variable, since you want to change the speed.

For handling starting the game with the same button, you can use a state variable, which contains a value of means "Game Stopped" or "Game Started".