I would like to reply that this happened to me today, and it is horrifying.
I was able to retrieve my files, but before doing that my entire downloads, desktop were unaccessble, I couldn't save or access anything, and even if I took a screenshot it would not download it.
Needless to say, the fact that syncing and installing DropBox literally compromises your entire machine is absurd and ludicrous and not worth any money whatsoever.