In an attempt to strengthen my site security, I changed the table prefixes from wp_ to a different prefix_. After doing so, the site and posts were still there but I was unable to access admin and got the message "You do not have sufficient permissions to access this page."
I searched the forum and found a couple of suggestions as to how to fix this, but nothing worked, so I tried to restore my site from the backup I had made using WP-DB-Backup. This failed too - the site has disappeared and when I enter the URL I am taken to a page to install WordPress - HELP!
My site included lots of videos and posts, which took months to do, so I would be grateful for any suggestions as to how I can restore everything.