Issue:

The form and script were working perfectly, but some days ago they have stopped working at all

How to solve:

This is the common case that the webserver administrador upgraded some of the software in the server, like PHP, Perl, ASP or email components, and the script require other settings in the configuration.

Specially, if your web hosting provider switches from PHP 3.x to PHP 4.x, you might have to check the Register Globals settings.

Also, due to continue email abuse, spam and viruses, webhosting companies are always straightening their mail servers to avoid such abuses, and maybe your scripts requires modifications.

Ask your System Administrator for changes in the webserver.