HELP Lightroom 5.6 Spontaneously Reboots Computer

Question

Lightroom 5.6 is installed on a new computer running Windows 8.1 and all drivers and software are up to date.  All other software is running fine including InDesign which has been used heavily for 5-6 hours without problems.  I imported my existing photos into a new catalog in a freshly installed Lightroom 5.6.  After Import, with minimal previews generated on all 11,400 images, I tried generating 1:1 previews on a small group of images and the computer spontaneously (no pause, no blue screen) just rebooted without any warning.  After the reboot I tried to start Lightroom again, received a message saying; “error in previews and Lightroom needs to close”.  Kept receiving this same message each time when starting Lightroom again and was unable to open Lightroom.  Uninstalled Lightroom and ran CCleaner to clear registry entries, cleared all Lightroom preferences and rebooted computer and then re-installed Lightroom.  Thinking that there may be some sort of error in the existing catalog I decided to start a new catalog and re-imported all images again.
(I have subsequently concluded that the error is in the Preview files. Apparently when Lightroom closes in a spontaneous reboot the preview files are corrupted hence the message I received. When the reboots happen during 1:1 preview creation I can successfully restart Lightroom if I first delete the Preview folder.)
After importing all images into the re-installed Lightroom tried creating 1:1 previews and experienced the same spontaneous reboot of the computer.  Thinking that there might have been some kind of error in the downloaded software, I downloaded a new copy of Lightroom 5.6 and re-installed the software (have done this twice now).  Again Lightroom spontaneously rebooted the computer when attempting to create 1:1 previews.  Uninstalled and reinstalled Lightroom in the manner previously described above.  After re-importing all images I decided NOT to create previews this time.  But as I was selecting an image in Library to show large, Lightroom spontaneously rebooted again; however this time I was able to restart Lightroom without receiving an error message.  After restarting Lightroom as I tried to select a new image in Library the computer once again spontaneously rebooted.
At this point I have uninstalled and re-installed Lightroom 5.6 eight times.  Each time I have carefully searched the computer to make sure that all vestiges of the previous installation have been deleted by using CCleaner, deleting ALL Lightroom folders and searching the registry to make sure that there was nothing left of the prior Lightroom installation.  I also deleted the catalog and all presets.  So at this point I am at a loss as to what my next step should be.
Any suggestions?  Thank you.
  Background: I started using Lightroom when Adobe purchased RAWshooter and upgraded all their uses to Lightroom version 1. So I have used every version through Lightroom 5.6. I have Lightroom installed on three other computers and they all run without an issue. This is the first time in all the years I have been using light that I have encountered any problem.

Answer 1

Thanks for the responses.
I have already installed HWMonitor when dj_page suggested it may be due to overheating yesterday.
Tried to insert a print sceeen but file was too big.
The CPU package is running at 62°C
the 4 cores vary from 61,62,64,54
I don't know if this is hot or normal.
Once I get into Lightroom I have no way of telling what the temps are as the second I generate a 1:1 preview the computer reboots.
All three case fans and CPU fan are running.
Don't know what else I can check.
The case is a mid-tower Antec with lots of space and well designed ventilation.
Currently I'm using the Intel graphics display built into the motherboard. Have a new graphics card coming because I suspect that the added load of the video onto the CPU may be causing the issue. What do you all think?