As Ruben mentioned above, it sounds like your includes/config.inc.php file got wiped.
When you restored the config file from your earlier backup, the file you restored may have had outdated settings in it. Always make sure to have a relatively recent backup of your files and setting.
I also see that you are on UBB.threads 7.6.0. You should look at upgrading to at least version 7.6.1, where the config file is automatically backed before any changes are being made and a new one is created.
UBB.threads 7.6.1 Changelog 2017-05-02
[NEW] The current forum config file is now backed up before new changes are saved. Normally there would be no need for this step, though an incorrectly configured server or php.ini setting may cause havoc and corrupt the new config file creation process. A forum owner can now roll back to their backup config file, if the new one was corrupted upon its creation.
SOURCE:
https://www.ubbcentral.com/forums/u...e-ubb-threads-7-6-1-changelog#Post260196
