Hola de nuevo!
Y gracias por contestar...
El caso que al poner
y presionar el botón, no me funciona. Entonces, para ver que error posible hay, he validado HTML y me da el siguiente error:
Cita: Validation Output: 1 Error
Required attribute "action" not specified
<form>
The attribute given above is required for an element that you've used, but you have omitted it. For instance, in most HTML and XHTML document types the "type" attribute is required on the "script" element and the "alt" attribute is required for the "img" element.
Typical values for type are type="text/css" for <style> and type="text/javascript" for <script>.
Supongo que habrá que poner <form action="..."> no?