OSX Yosemite constant reboot

Question

Hi,
Since installing Yosemite my mac mini (Mid 2011) will only get 10-20% into the start up process before shutting down like some pulled the power cable out the back. It then proceeds to try and boot again but with the same result over and over. I can get into safe boot and it stays on, the console lists shutdown cause as -128.
Dec 24 01:10:11 Marks-Mac-mini kernel[0]: Previous shutdown cause: -128
Dec 24 01:20:50 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 01:31:52 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 01:39:49 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 01:45:02 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 01:49:27 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 01:53:37 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 02:00:32 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 02:05:29 localhost kernel[0]: Previous shutdown cause: -128
Dec 24 02:08:52 localhost kernel[0]: Previous shutdown cause: -128
Prior to the Yosemite install I had run OS X Lion for 3 years without any issue, the system has been rock solid. I did a clean install of Yosemite, did the usual disk check/repairs and have since tried again resetting PRAM, SMC, ran Apple diagnostics multiple times but to no avail, all results come back as ok. Been a Mac user for over 20 years and never seen this before, I don't understand how a system change can kill a computer like this but I'm out of ideas.
Mark

Answer 1

There may be more than one issue, but a negative shutdown code, if it happens repeatedly, may indicate a hardware problem. The precise meaning of the codes is not publicly documented.
If you haven't already done so, you can try resetting the System Management Controller. Otherwise, or if the reset has no effect, see below.
Make a "Genius" appointment at an Apple Store, or go to another authorized service provider. You may have to leave the machine there for several days.
Back up all data on the internal drive(s) before you hand over your computer to anyone. There are ways to back up a computer that isn't fully functional—ask if you need guidance.
If privacy is a concern, erase the data partition(s) with the option to write zeros* (do this only if you have at least two complete, independent backups, and you know how to restore to an empty drive from any of them.) Don’t erase the recovery partition, if present.
Keeping your confidential data secure during hardware repair
Apple also recommends that you deauthorize a device in the iTunes Store before having it serviced.
*An SSD doesn't need to be zeroed.