Dropbox never finishes spinning
If Dropbox never finishes spinning on your Mac, it means there are some files it can't transfer, or is repeatedly transferring.
Sometimes this is because your network is too slow and your files are too big. Maybe check that first. Generally, if you have files over 1 GB in size that you are trying to back up, you probably want to have over 50 Mbps network speed.
If however it is not filesize that is the issue, in order of drasticness, try the following:
1. Rebuild privileges
a. Click on the dropbox menu icon
b. Click on your personal avatar/icon
c. Click on Preferences
d. Alt-click on Account
e. It will bring up a bunch of buttons one of which is repair privileges. Click it.
f. It will ask your admin password. Give it. Depending on how many files you have, this will take a few minutes. I have about 1m files (really) and it takes about 10 minutes.
2. Find and delete linkfiles
a. Open a Terminal
b. Type:
cd ~/Dropbox ; find ./ -type l -delete
where "l" is an ELL, not a One.
3. Turn off antivirus (temporarily)
Dropbox servers don't stop you uploading viruses. BUT if your copy keeps trying to download and sync viruses to your Mac, AND they keep getting quarantined and deleted by your antivirus software, Dropbox will try download them again, etc etc etc forever. You need to therefore figure out which files contain viruses and delete them ON THE DROPBOX WEBSITE first. Turn off antivirus, let it finish downloading, see where the viruses are in the records/log of your antivirus, and then go to dropbox website, delete those files, and then turn antivirus back on.
4. Reset Dropbox to initial conditions
a. Quit Dropbox
b. Open a Terminal
c. Type:
cd ; rm -rf Dropbox/.dropbox ; rm -rf ~/.dropbox
d. Re-open Dropbox
e. It will ask for your login details etc., again as if you had just installed it for the first time. This should, in theory, not cause any problems for you, except you MIGHT find duplicate files as a result, called "conflicted copy". Generally the file called "conflicted copy" is the NEWER file.