[Lynne]

Have you checked your error_logs (if you don't know where they are, ask your host)? Have you tried reuploading the default vbulletin files for your admincp? Have you tried disabling your plugins and then trying to edit a template?
Note: To temporarily disable the plugin system, edit config.php and add this line right under <?php

PHP Code:

define('DISABLE_HOOKS', true); 


Don't forget that for vbseo, disabling the modification means to also get rid of anything extra you added to your htaccess file.