To fully reset the settings produced by OFP's Preferences program, delete file Flashpoint.cfg in OFP's base directory. Then rerun the Preferences program and click on AUTODETECT to create new copy of the file.
To fully reset the settings made from within the OPTIONS main menu selection, delete file USerinfo.cfg in subdirectory \Users\your_player_name\. The next time you run OFP, a new default copy of file Userinfo.cfg will be created
Both file Flashpoint.cfg and Userinfo.cfg are text files that can be edited with any standard text editor, if you feel qualified to do so.