I just set up a new Dropbox account with a different email. When it asked whether I wanted to sync/back-up Desktop, Documents and Downloads folders, I said no, because when I did this with a previous account, this caused problems. I thought that this would mean that my Desktop files etc would just remain on my hard drive, and I would have a Dropbox folder with things I wanted to back up to the cloud.
But this has caused all the icons to disappear from my Desktop!
Luckily the files are still there when I search for them. When I got to Desktop folder in Finder and click on it, a message says 'The operation can’t be completed because the original item for “Desktop” can’t be found.'
Logging out of Dropbox didn't help.