Why does my iMac reboot every day at the same time? Every evening around 10:30, my iMac just stops and restarts. It's not a power outage because another iMac next to it (same plug) is not affected. 

I'm thinking maybe a service that's set to run at that time, but I don't see it just shutting down the computer with no warning ..
This is a shot in the dark but worth checking, since it is so specific time wise, have you maybe by accident set up an automatic restart under the Energy Saver?


Open Preferences
Open Engery Saver
Click on Schedule