Nasty, bad luck!
Can you get to the command line/shell on it? If so try
php console.php cache:clear (again) to clear the caches, then maybe
php console.php database:update (again probably) which might help.
The next step usually is to look in the apache error_log if you can, and if you can't then try setting the error reporting in the installer to show everything for non-admins, that might uncover the problem...