Cita:
Iniciado por pateketrueke 
si... observa
header("Location: {$_SERVER['HTTP_REFERER']}");
o...
header("Location: " . $_SERVER['HTTP_REFERER']);
Hola, gracias por ayudarme.
Bueno he usado estas dos opciones que me das y entonces me sale el siguiente error:
Warning: Cannot modify header information - headers already sent by (output started at /home/santodom/public_html/config.php:12) in /home/santodom/public_html/entrar.php on line 28
Warning: Cannot modify header information - headers already sent by (output started at /home/santodom/public_html/config.php:12) in /home/santodom/public_html/entrar.php on line 29
Warning: Cannot modify header information - headers already sent by (output started at /home/santodom/public_html/config.php:12) in /home/santodom/public_html/entrar.php on line 30
Warning: Cannot modify header information - headers already sent by (output started at /home/santodom/public_html/config.php:12) in /home/santodom/public_html/entrar.php on line 31