Screenshot go 'nowhere' after Dropbox installation
To check where screenshots are currently assigned, in Terminal type

defaults read com.apple.screencapture location


By default that would actually return no answer, as the line should only be written if you ever change it - so I'm assuming Dropbox did change it at some point.

To reset it to the default desktop location, type  

defaults write com.apple.screencapture location ~/Desktop


followed by  

killall SystemUIServer


This should cover for  Cmd ⌘   Shift ⇧   3  &amp;  4  screenshots. Screenshots to clipboard should be unaffected, &amp; still be activated by adding  Ctrl ⌃  to either of the above methods.