I installed all of the august 12 updates today, after the first reboot everything seems fine. After a second manual reboot that wasn't requested, they system shows the initial flag and loading throbber, then kicks to an all black screen and gets no further.
System restore fixed the problem, I have reinstalled some of the updates so far, and found some are ok, but at least two are definitely still causing this black screen on second reboot.
Security Update for Windows 8.1 for x64-based Systems (KB2982791)
will cause this issue on it's own.
Update for Windows 8.1 for x64-based Systems (KB2975719)
will also cause this even if KB2982791 is not installed.
All other updates from windows update are installed currently.
One of these is also causing the issue even when KB2975719 is not installed.
I'm going to be slowly trying to install and test to find out which, but it's time consuming and I'm hoping to get the ball rolling finding the problem sooner.
win 8.1 x64, Pro with Media Centre
asus z87-m plus, bios 1005
PCIe SB X-Fi Titanium, Driver version 2.40.8
nvidia gtx 750ti , 340.52 whql
Other 3rd party drivers/background apps:
razer synaps 1.18
ASUS_AMDA00_ACPI for Windows 8.1 (2014/01/06)
It's a very, very clean system overall.
edit: Nothing but a few apps and MS redists required for them, no additional firewall or antivirus over what is built in.
*edited to remove updates that have been eliminated as causes.