can't drag files to hard drive after High Sierra install

After installing High Sierra, I can't drag files off desktop onto hard drive. Get error: "Modifying ____ requires an administrator name and password." This happened before with other OS updates, and I could always right-click on the hard drive icon, Get Info, and change the permissions to fix it. In the Get Info window for my Home and hard drive, I am no longer listed as an administrator. When I try to add myself back in, I get this: "The operation can't be completed because you don't have the necessary permission."

I have tried "Apply to enclosed items" and then running this in Terminal: diskutil resetUserPermissions / `id -u`

Still can't drag items to hard drive without entering a password. Any fixes out there? Thanks for any assistance.