kiwifidget:

 

Everything already up to date, and all tests passed.

 

I noticed an audible fan noise during the cpu test.

 

Pretty sure I've heard that same noise about the same time the clock stops.

 

I've heard cooling fans spin up when there is a problem a number of times.  I figure its some kind of fail-safe thing.

Is it practical to erase the machine and set them up with a fresh Windows installation?  If it works fine, you've eliminated a hardware fault.  If the same thing happens, it's most likely a hardware fault.  With the machine being under three years old you could take it back and ask for it to be repaired, but the first thing they will likely want to do is factory reset the software.

One thing to try while I think of it.....  do CHKDSK (did you do this earlier?) and then an SFC / SCANNOW

Use SFC Scannow to Repair Windows System Files (lifewire.com)