yeah, check the apache logs! probably your error reporting is off, it might be setting in your php.ini file (you can run php --ini to see files being used if you have shell access to server), just remember, there might a separate php.ini file used for running php shell from with command and separate for when it's run through web, just remember, get the right php.ini - this will show you errors :) and then you can see whats wrong with your app... on a linux server logs should be in /var/logs/httpd(or apache2 depending on your version)
btw. check this one http://php.net/manual/en/function.error-reporting.php