WatchDog on Arduino Nano - does not recover
This works on an Uno R3.

The sketch restarts every 4 seconds when wdt_reset() is commented out.

Please copy the code and try it.

  #include &lt;avr/wdt.h&gt;

  void setup() {
    pinMode(13,OUTPUT);
    digitalWrite(13,LOW);

    delay(50);
    digitalWrite(13,HIGH);    // flicker the LED to identify when setup() is running
    delay(50);
    digitalWrite(13,LOW);
    delay(50);
    digitalWrite(13,HIGH);
    delay(50);
    digitalWrite(13,LOW);
    delay(50);
    digitalWrite(13,HIGH);
    delay(50);
    digitalWrite(13,LOW);
    delay(50);

    wdt_enable(WDTO_4S);

  }
  void loop() {
    digitalWrite(13,HIGH);
    delay(500);
    digitalWrite(13,LOW);
    delay(500);
    //wdt_reset();
   }