I'm sorry to be starting another of these threads, but I'm super frustrated. Every so often this seems to happen on all my Macs, where suddenly it will stop going to sleep. This time it will not sleep whether at scheduled time or when I tell it to sleep from the Apple menu. It started doing this today when I was trying to figure out a problem connecting my monitor to a Caldigit Thunderbolt Station. I'm running 10.9.1 on a 2012 Mac Mini. This is what I've tried: reset SMC rest PRAM repair permissions clear caches reindex Spotlight and finally reinstall OS There is nothing in the system log related to sleep. I've simplified everything so there are no additional peripherals attached to the Mini, removing the Thunderbolt Station and putting the monitor back on the Thunderbolt port. I don't know what else to try.