I also constantly run into this issue on Windows 8.1 64bit running on an ASUS Z97-K:
The computer shuts down 75% of the time, either while entering the Bitlocker passwort or soon afterwards but before I get to the log-in prompt.
These are two cases in which this happens that appear distinct:
a) If I do not touch the keyboard, the computer always shut down exactly 60sec after the Bitlocker password prompt appears.
b) If I touch the keyboard (type in my password, or even just hold the shift key), the computer shuts after a variable length of time. While trying this a few times just long and starting to hold the right shift key as soon as the password prompts appears, I encountered times between 3 and 15sec before the shutdown.
If I do make it to the Windows log-in prompt, the computer then runs stable (have run it for many hours, inclusion games, and have ample power and thermal reserves remaining).
I tried the suggestions from this thread but they have not fixed the issue:
1.) I just updated my Z97-K BIOS to the latest version 2502 from Feb 2015 (previously version was 0330); I had Bitlocker suspended during the update so it didn't prompt me for the password during the next startup and it started successfully, but then then next four starts failed (shutdown while entering password).
2.) Just in case, I also installed the latest Intel chipset driver from the ASUS website.
3.) Since I have a lot of RAM (32 GBytes), I checked whether Windows has already virtual memory allocated; it had, namely about 4 GBytes.
4.) The EventViewer under Administrative Events has one pre-shutdown Warning event that might be revelant:
[04/03/2015 22:58:19] Warning: The driver \Driver\WUDFRd failed to load for the device ACPI\PNP0A0A\2&daba3ff&2.
The next two Administrative Events are from the next boot:
[04/03/2015 23:33:39] Error: The previous system shutdown at 22:58:21 on 04/03/2015 was unexpected.
[04/03/2015 23:33:36] Critical: The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.
After further digging, the warning above relates to the ACPI Probe II sense driver (AMDA00) on ASUS boards. According to Device Managers / System Devices / AMDA00, this device was (currently) running successfully at driver version 1.0.0.0. I then installed ASUS Probe II Sense Driver 1.0.1.0 from the ASUS website (not part of the Intel Chipset Drivers).
Two of the next three boots were successful (might be chance). In the third case, the computer shut down again while I entered my password, but the EventViewer this time didn't list any of the above pre- or post-failure messages.
Does anyone have any additional ideas?
I thought I had solved this but it came back again, albeit more randomly now.
I am stumped I have tried all I can think of as well as all the suggestions to no avail.
I really cannot see a pattern from a timing perspective, it can happen as soon as I start to put the password in or at anytime during that process. The good news is I have always been able to get in eventually, I think 6 times was the most attempts.
The incidences became fewer after I updated the BIOS but it still occurs, just not every time. Bizarre.
It does remind me of what happens when a PC is overheating, but since it only ever happens when I boot for the first time in a day (never in subsequent boots after software update etc) it can't be that UNLESS the PC THINKS it is overheating (BIOS ?).
I am all ears to suggestions, just worried that one day it might lock me out completely (not yet after 18 months).