Beach ball all the way and the iMac won't restart. Restart will crash the finder and mean the only way to reboot switch the power button. Safari is s-l-o-w-w-w. Finder is having trouble doing simple tasks. Like typing this! Dropbox syncing seems to be part of the problem, but then nearly all apps take forever to load up. This is after a replacement drive (iMac fusion replacement program) - am I just being an idiot blaming El Capitan here?