Something happened on my iMac last night... I found the finder, dock, and more and more unresponsive, So I restarted, and the boot up wouldn't finish. It being super late, I just didn't want to deal with it, so saved it for today. Unplugged everything, tried, same thing...booted from an older backup (no curent one ) and it booted fine, and ran disk utility and that showed things were good. Ran disk warrior, that showed fine. Booted back to main drive, in safe mode, brought me to the user select screen, and the main user account I couldn't get in... it would start logging in and beach ball. But the Guest account it went fine. I set up a new account, but it would beach ball when I tried to get into that one. Verbose mode runs thru the writeouts, then gets to the same point and beach ball. I've spent the past X hours copying the drive contents to a new backup, and have downloaded El Capitan installer.. I figure the best idea is just to try to reinstall over the current and hope that fixes the issue, otherwise, do a clean wipe and install and go from there, rather than going deeper and deeper into fix and troubleshooting, BUT, I wanted to poll the brain trust if anyone has any thoughts I should try.