After uninstalling and reinstalling the dropbox app, I could not get the desktop app to connect back to my account. It would keep getting me the message: "computer is currently offline", even though my internet was functioning correctly. After several hours I found the reason and the only solution that will work.
1. logon to your dropbox account on a web browser.
2. go to settings > security
3. scroll down to devices
4. find the device (desktop or laptop) that you are trying to connect, and delete it
5. restart your router
6. restart your computer.
7. make sure that your computer time and date are synced and accurate with the time zone that you're at now.
Now try to click on your desktop app, and it should prompt you to link your dropbox account to your desktop application.
Good luck!