My WP site is hosted on a Parallels virtual machine hosted at Blacknight. I used their control panel to upgrade to 3.8.1 - it was 3.6.something. I had previously used AIOWPS to change the database prefix, but the update changed the table_prefix entry in the wp_config file back to wp_. The result is an empty WP with just the default Hello World page.
In the database there are two sets of tables, one with the wp_ prefix and one with the more secure prefix. I have edited in the database the wp_posts table and changed the post name from Hello world to Bonjour, and the change shows up on the web page, so WP access to the database is working. But if I change the table_prefix entry in the wp_config file from wp_ to the more secure prefix, the web page just comes up blank. What am I missing?