Get when a button close the circuit That seems to be a bit stupid to myself but I can't figure out to get to know when my button is pushed (closed) or released (open). 

You must know that this not just a simple push button. Actually it is more of a complex button with multiples output (Y, G, 0V, COM, NO, NC, HORM, 12V). 
With a multimeter i've been able to locale witch output are closed when the button is pressed. These are HORM (that is the name for two outputs -?!-) and on the other side COM and NO.

I've tried to plug that to my arduino Mega, on PIN 7, and getting the value with Digital.Read. Tho when i try to display it on the Serial, it doesn't work and return an error. (It did the same for HORM and COM/NO) 

I also noticed something strange. When the button is pressed, Arduino seems to notice it because my "ON" led turns off and then turns back on. Like if the arduino was crashing. The 13th pin LED stay HIGH after the arduino goes back on. 

Please, have a look at my code. 

int ledPin = 13; // choose the pin for the LED
int inPin = 7;   // choose the input pin (for a pushbutton)
int val = 0;     // variable for reading the pin status

void setup() {
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);  // declare LED as output
  pinMode(inPin, INPUT);    // declare pushbutton as input
}

void loop(){
  val = digitalRead(inPin);  // read input value
  Serial.write(val);
  if (val == HIGH) {         // check if the input is HIGH (button released)
    digitalWrite(ledPin, LOW);  // turn LED OFF
  } else {
    digitalWrite(ledPin, HIGH);  // turn LED ON
  }

  delay(1000);
}


Do you guys have any advice ? 

Thank you very much in advance. 

Also please have a look at the circuit. The only difference is that instead of having this kind of simple pushbutton, i've got my NO and COM plugged the same way.
Ok then. 

I just tried that again and it simply seems that the wiring shown on the tutorial is not good at all. 
I made another wiring that worked exactly fine.