How can I “reset” an Arduino board?

Question

I\'ve uploaded a sketch to an Arduino Uno whose loop is something like this:

void loop(){
    Serial.println(\"Hello, World!\");
}

So, now,

Answer 1

For Arduino Yún users, try uploading via Ethernet/Wi-Fi (menu Tools → Port).

I had exactly the same problem, and I tried pretty much everything (apart from burning a new bootloader). I am surprised it worked, but I've uploaded an empty sketch without any problem.