A modified configuration settings file cannot be restored to a previous state. Something on your machine, typically a virus protection or "system cleaning" utility application, has erased or damaged files wrongly. A typical issue on Windows installations.
The settings file is AppData\Roaming\Pleiades\PixInsight.ini under your home folder. You can make a backup of this file if you want, but you'd better fix the issue by properly configuring your system and its utility applications.
