Could you try to regenerate the form from scratch, thanks to the form builder? You should get a shortcode similar to this one:
[contact-form][contact-field label='Name' type='name' required='1'/][contact-field label='Email' type='email' required='1'/][contact-field label='Website' type='url'/][contact-field label='Comment' type='textarea' required='1'/][/contact-form]
Let me know if it helps.
After the regenerating I got this:
CRASH: PHP segmentation violation in preg_replace_callback() called at [/autoinstalator/wordpress/wp-includes/shortcodes.php:188], in do_shortcode() called at [/autoinstalator/wordpress/wp-content/plugins/jetpack/modules/contact-form/grunion-contact-form.php:589], in Crunion_Contact_Form_Shortcode::parse_content() called at [/autoinstalator/wordpress/wp-content/plugins/jetpack/modules/contact-form/grunion-contact-form.php:576], in Crunion_Contact_Form_Shortcode::__construct() called at [/autoinstalator/wordpress/wp-content/plugins/jetpack/modules/contact-form/grunion-contact-form.php:746], in Grunion_Contact_Form::__construct() called at [/autoinstalator/wordpress/wp-content/plugins/jetpack/modules/contact-form/admin.php:466], in grunion_ajax_shortcode() called at [/autoinstalator/wordpress/wp-includes/plugin.php:429], in call_user_func_array() called at [/autoinstalator/wordpress/wp-includes/plugin.php:429], in do_action() called at [/autoinstalator/wordpress/wp-admin/admin-ajax.php:82]
Could you try to follow the instructions here to find out if the issue is caused by a specific plugin?
http://codex.wordpress.org/Common_WordPress_Errors#The_White_Screen_of_Death
Let me know what you find out.
