Hi Megan and Mark: I had already done that hours ago - found the "Autoplay" and changed both the "Removable Drive" and "Memory Card" options to "Use File Explorer to view the files". I went back just now and and double checked. The move from my hard drive to Camera Uploads is still occurring.
Again, what is happening here is Dropbox is going through my new PC's HARD DRIVE (a 2TB SSD), finding photos and backing them up to "Camera uploads". On my hard drive I have the photos separated into folders by years, e.g. "2016", "2017", etc. I know this sync is occurring because I only keep the latest year to 18 months of photos in my Camera Uploads, but now that folder has photos from 2016. And I keep getting that message "importing photos, about 25 hours left" although the time is coming down. And when I go to "Task Manager", I see Dropbox consistently using 25Mb/second of network.