I've changed the php-script to how it was in the first post.
And I've installed USBWebServer (my brother said I should install it because it would take too long to upload the site everytime I changed something).
And now I get this:
Warning: mail() [function.mail]: Failed to connect to mailserver at "localhost" port 25, verify your "SMTP" and "smtp_port" setting in php.ini or use ini_set() in C:\Users\Musti\Desktop\USBWebserver v8_nl\root\Inschrijven1.php on line 33
And Johanafm, you also brought up php.ini. But I don't have a php.ini file? My whole site is in html except the file for sending the forms.
Btw, this is line 33:
$success = mail($webMaster, $emailSubject, $body, $headers);