DropBox won't open files

I'm disappointed to see there was no reply when I answered your questions.  I have apparently solved the problem, but I am quite disappointed in how Dropbox seems to handle files.  I looked at the history of the files in question and found that I did indeed modify them, unintentionally.  And that was the case even for files I had previously deleted!  It turns out that when I got my new computer and moved all my files from the G drive on the old computer to the D drive on my new computer, it corrupted the files in my Dropbox list in File Explorer on the new computer...even though most of the files there had been copied / pasted into those folders on the original computer.....so apparently they weren't really pasted in, just a link to the original location.  While thus corrupted, the file names still showed in File Explorer so I had not checked to see if they opened.  Had I done so, I would have seen that they do not, and thus the versions on the Dropbox website were also corrupted.  Note again that even the files shared from fully 40 other users in my Dropbox were also corrupted by me getting a new computer, even though I had previously deleted their files!!! Those shared files were also corrupted in the Dropbox accounts of all those 40 users!!!  Obviously they were not happy with me.  Fortunately I was able to Restore all the files to their original state from before my changes.  That got everyone working again.  Lessorn learned on how Dropbox apparently works.  My mistake, but still, I don't think Dropbox should have taken it that far, especially on deleted files.