What other tool is using my hotkey? [duplicate]
If you are on Windows 7 or below, you could try the free Windows Hotkey Explorer. Do not run it on Windows 8 and later, as it will execute every registered hotkey.
It's the second program/link on that page. It shows you which program has registered you hotkeys.
https://www.dropbox.com/help/1964/en
You can always turn this feature on or off in the application's preferences:
Click the Dropbox icon in your menu bar.
Click the gear icon and select Preferences… from the menu.
Click the Import tab.
Check or uncheck Share screenshots using Dropbox.