First of all, I can't drag anything anymore from Windows Exporer to my Project. That is ok, I can still import. But here is the strange thing: I can't drag anything AT ALL inside the project anymore. I created a bin called "videos", imported videos outside of the bin, and I can't drag the videos I imported to the new bin. I can't drag anything inside it. It's all locked.
Ok, I just experienced this for the first time....very frustrating...But, I closed all undocked panels...then just re-opened my "Project"panel window and began moving clips into bins, etc. like normal in dual screens.
Thank you, @Todd5FCA! I had the same issue. My entire interface seemed crippled, but your solution worked perfectly. I closed all panels and then reset them by using the menu "Window > Workspaces > Reset to Saved Layout" to bring them back and all seems fine now. Much appreciated!