johnbl :
start cmd.exe as an admin then type the following commands
cd c:\
dir /s *.dmp
this will search for memory dump files, sometimes if windows makes a live dump for diagnostics it will put it in a different directory so it will be uploaded to microsoft for debugging and so a fix will be pushed out to your machine.
Last time I looked at this on someones machine it was caused from certain USB chips on the motherboard that required specific usb drivers. Windows made a live kernel memory dump because the USB controller stopped responding and the machine was rebooted to get it to function again. Root cause was they system needed to update the BIOS and update the chip driver. Too bad there was no BIOS update or driver update for the machine. We ended turning off the USB 3.0 host controller via BIOS just to prevent the machine reboots every day. I did not figure out the problem until we searched the system for .dmp files and took a look at one being sent to microsoft.
This is what I got after following your direction with the command prompt. I've been having the same issue with random complete shutdowns with no notification. Seemed to start after I installed the very large November Windows 10 update to build 10586. I have HW Monitor and I haven't seen any abnormal temps, either.
Microsoft Windows [Version 10.0.10586]
(c) 2015 Microsoft Corporation. All rights reserved.
C:\Users\GarthVader>cd c:\
c:\>dir /s *.dmp
Volume in drive C has no label.
Volume Serial Number is 5CAA-239A
Directory of c:\ProgramData\Microsoft\WDF
08/31/2015 05:53 PM 131,896 DriverManager_1612.dmp
09/22/2015 03:28 PM 116,400 DriverManager_1760.dmp
2 File(s) 248,296 bytes
Directory of c:\ProgramData\Microsoft\Windows\WER\ReportQueue\AppCrash_Explorer.EXE_12a53f408a4c4482eeb261651dfa88fa560fa16_43dcc54e_cab_1da0b2d1
12/02/2015 10:53 AM 612,336 triagedump.dmp
1 File(s) 612,336 bytes
Directory of c:\Users\All Users\Microsoft\WDF
08/31/2015 05:53 PM 131,896 DriverManager_1612.dmp
09/22/2015 03:28 PM 116,400 DriverManager_1760.dmp
2 File(s) 248,296 bytes
Directory of c:\Users\All Users\Microsoft\Windows\WER\ReportQueue\AppCrash_Explorer.EXE_12a53f408a4c4482eeb261651dfa88fa560fa16_43dcc54e_cab_1da0b2d1
12/02/2015 10:53 AM 612,336 triagedump.dmp
1 File(s) 612,336 bytes
Directory of c:\Users\GarthVader\AppData\Roaming\Mozilla\Firefox\Crash Reports\pending
04/08/2012 04:15 PM 76,544 00e338a2-8120-4f4a-98e8-1dfe2bcb9ffe.dmp
06/02/2014 04:13 PM 208,756 896b57c1-865a-42d8-b29e-f381f86104b8-browser.dmp
06/02/2014 04:13 PM 38,515 896b57c1-865a-42d8-b29e-f381f86104b8-flash1.dmp
06/02/2014 04:13 PM 64,905 896b57c1-865a-42d8-b29e-f381f86104b8-flash2.dmp
06/02/2014 04:13 PM 52,521 896b57c1-865a-42d8-b29e-f381f86104b8.dmp
02/28/2015 10:14 PM 60,061 a9cee23f-7853-44bb-9acb-a275d769b64d.dmp
04/23/2014 07:20 PM 20,418 dee0ae53-1047-4d51-8c38-c7b3880c18a8.dmp
03/17/2015 08:05 PM 280,165 e1fe5dc9-c22b-41ac-a0f4-5cfe66ff65f3-browser.dmp
03/17/2015 08:05 PM 38,781 e1fe5dc9-c22b-41ac-a0f4-5cfe66ff65f3-flash1.dmp
03/17/2015 08:05 PM 88,247 e1fe5dc9-c22b-41ac-a0f4-5cfe66ff65f3-flash2.dmp
03/17/2015 08:05 PM 52,631 e1fe5dc9-c22b-41ac-a0f4-5cfe66ff65f3.dmp
11 File(s) 981,544 bytes
Directory of c:\Users\GarthVader\AppData\Roaming\Mozilla\Firefox\Profiles\zmqu1q35.default\minidumps
01/07/2014 04:28 PM 0 0b50580f-3785-4e88-a9e7-7c27e1a5f3a0.dmp
09/17/2012 07:52 PM 0 0b685356-b3fd-4d73-9015-04ce6098f713.dmp
06/05/2013 10:16 AM 0 130ae1f0-8652-43f6-8ff3-eb7e885c16dd.dmp
09/13/2012 10:57 PM 0 1c053d51-8d70-4799-bd00-9208652be1cc.dmp
06/24/2012 04:50 PM 21,412 218965a2-b86a-4df2-bb7f-d71d491c48e5.dmp
01/03/2014 05:26 PM 0 38df2f32-a22f-474d-8b3a-e119a4b7a41d.dmp
05/03/2014 11:47 AM 0 4907c857-6259-48ef-8f14-9b82fab31ed1.dmp
03/12/2014 02:20 AM 0 603e8a80-50ec-45bc-b920-7f37db7e8dda.dmp
04/04/2014 10:58 AM 0 64cf48e2-3800-4eaa-bcd2-b252b2091f02.dmp
02/13/2014 09:26 PM 0 90b6553a-27cc-4276-acaa-354e1781b388.dmp
01/10/2014 07:23 AM 0 ada71067-5790-4170-857a-9347e4da0427.dmp
01/08/2014 03:42 PM 0 b237ffb9-341f-428d-a59d-f89aa79436de.dmp
01/06/2014 12:59 PM 0 ba16d6ab-d79f-442d-aa14-e979743936d7.dmp
09/23/2012 02:16 AM 0 ce89436c-eeaf-42e3-a4c9-8a1f0ed21870.dmp
05/02/2014 02:16 AM 27,594 e07d88ca-cd40-4ca4-af2a-789f890ee1c7.dmp
04/17/2014 08:54 PM 0 e6e164a5-16b5-4457-944d-7416adec0701.dmp
03/24/2014 06:37 PM 0 eb100913-f27d-4e96-adb5-38d6c862d1f1.dmp
09/23/2012 02:16 AM 26,756 f982da9e-0d21-4d7b-859a-6b8be7040a9c.dmp
18 File(s) 75,762 bytes
Directory of c:\Users\Noy\AppData\Roaming\Mozilla\Firefox\Crash Reports\pending
02/26/2012 12:47 PM 79,304 3e606971-9c8e-4742-96fa-ccb4c76a9136.dmp
02/26/2012 12:47 PM 136,803 5afa9a62-c87c-487d-bcae-80f77fc93d97.dmp
04/14/2012 10:05 AM 84,945 999095cf-2599-45de-91f1-047d9dd486f7.dmp
04/14/2012 10:05 AM 155,451 be8639cc-11d9-4555-8526-b875cf7eaaed.dmp
4 File(s) 456,503 bytes
Directory of c:\Users\Pzarks24\AppData\Local\CrashDumps
01/12/2012 03:36 PM 534,795 LifeFrame.exe.3708.dmp
01/12/2012 03:35 PM 534,795 LifeFrame.exe.4248.dmp
01/12/2012 03:37 PM 534,795 LifeFrame.exe.4900.dmp
01/18/2012 09:21 PM 24,566,045 Skype.exe.3080.dmp
4 File(s) 26,170,430 bytes
Directory of c:\Windows.old\Users\All Users\Microsoft\WDF
08/31/2015 05:53 PM 131,896 DriverManager_1612.dmp
09/22/2015 03:28 PM 116,400 DriverManager_1760.dmp
2 File(s) 248,296 bytes
Directory of c:\Windows.old\Users\All Users\Microsoft\Windows\WER\ReportQueue\AppCrash_Explorer.EXE_12a53f408a4c4482eeb261651dfa88fa560fa16_43dcc54e_cab_1da0b2d1
12/02/2015 10:53 AM 612,336 triagedump.dmp
1 File(s) 612,336 bytes
Total Files Listed:
46 File(s) 30,266,135 bytes
0 Dir(s) 447,439,421,440 bytes free
c:\>