Chosen Solution
Hello! Backstory: I purchased a late 2014 Mini about a year ago and attempted to setup bootcamp with Windows 10. Following numerous failed attempts I made an appointment with a genius bar. After several more attempts by three different geniuses over the span of 3-4 hours, they were finally able to get Windows installed. Flash forward a couple of months and Windows pushes out one of its big cumulative updates. I try to install the big update and it errors out over, and over, and over. After scouring Google for days and trying a variety of suggestions I decided to throw in the towel and give up on bootcamp altogether. But, somehow during the process of removing the Windows partition, I also managed to destroy the macOS partition along with the recovery partition. (yes, I am an idiot). Feeling extremely frustrated, I stuck the mini on a shelf and moved on with life. Flash forward to today. I removed the Mini’s hard drive, hooked it up to my iMac, and reinstalled macOS. Put the hard drive back into the Mini, fired it up, and … it won’t boot! The LED comes on, I hear the startup chime, but my display remains black. Then, after 20-30 seconds the Mini powers itself off. Any ideas of where I should start? What is the most likely thing I screwed up? Thanks!
You’ll need to set a bootable OS installer USB thumb drive so you can properly update your Mac mini. Here’s how: How to create a bootable macOS Mojave installer drive You have two issues the first is your iMac updated the drive to APFS on you, yet your Mini has no knowledge how to boot up under it as the systems firmware was not updated. Upgrading the system from your installer drive should fix things.
I think somewhere down the line you may have damaged your SMC. Does the mac mini display on any of the other output devices like HDMI or Thunderbolt?
