First try enabling maximum error reporting in your admin. To do this you will need to manually edit your <joomlabase>configuration.php and set the error_reporting to maximum:
public $error_reporting = 'maximum';
It is probably set to default. This should give you a proper PHP error and from that we can determine what's wrong. If that doesn't work check this site out:
www.phoca.cz/documents/16-joomla/336-how...g-php-errors-on-site
it will provide some info on how to enable PHP error logging via php.ini.