iCloud Drive Isn't Working

Hey Gang,

iCloud Drive stopped working on my iMac running Yosemite 10.10.2. There's nothing that I can remember that would break this except for the fact that I just go a new iMac and starting setting that one up. That one said "Setting Up" in the iCloud Drive folder for a couple of hours so I can cancelled it and restarted the computer. Now neither of the two iMacs will synchronize files with iCloud Drive, and my MacBook Pro stopped synchronizing as well. Interestingly enough, my Windows machine running iCloud Drive is still synchronizing just fine.

The files are still on my iMac, but they are not synchronizing with the files on iCloud.com. In addition, all the files shows the cloud icon in the Finder but none of them show the download/upload progress bars that I'm used to seeing. I have tried signing out of iCloud and deleting all files, then signing back in. I've deleted the "Mobile Documents" folder, but none of these work. Is there something I'm missing here?

Thanks for your help.