Classic CC Refuses All Commands

I am experiencing what seems to be an old problem that requires me to rename the "lightroom 6 Preferences.agprefs" file before I can continue using the program.  The problem has the same symptoms as when the "copy settings" window is hiding behind another window.  I'am using a high-end Dell desktop with compatible Graphic card, solid state drive, tons of RAM, etc.   I can't find anything current on this topic in Adobe support.   Been using Photoshop/Lightroom CC for over a year.

Thanks for any help ... Keith