Thanks to droolinggeezer. Yes for the older mac mini, it need to disable all option to the power saver. It worked for me on the latest 2014 mac mini. Solved my rebooting issue after the fresh new hard drive (hd) installed. I thought the hd had issue but it’s not. It had the same issue with the new replaced hd. I am not sure why Apple does not know about this issue and do something to fix this issue? I will raise this issue the Apple tech support. They were on the phone with me for 1.5 hour trying to install and reinstall the macos operating system.