I am having the same issue with my computer randomly suddenly turning off with NO Warning after upgrading to Windows 8.1.
I was just looking at my Event LOGS and see an Error Event about the time this just happened. it has something to do with Windows Live Communication Application Failure. I believe that is the source of the issue.
Here is the Error...
The program LiveComm.exe version 17.5.9600.20461 stopped interacting with Windows and was closed. To see if more information about the problem is available, check the problem history in the Action Center control panel.
Process ID: f9c
Start Time: 01cf70b2b369b09a
Termination Time: 4294967295
Application Path: C:\Program Files\WindowsApps\microsoft.windowscommunicationsapps_17.5.9600.20461_x86__8wekyb3d8bbwe\LiveComm.exe
Report Id: a80b1f8f-dca6-11e3-affa-00508d7ab4d9
Faulting package full name: microsoft.windowscommunicationsapps_17.5.9600.20461_x86__8wekyb3d8bbwe
Faulting package-relative application ID: ppleae38af2e007f4358a809ac99a64a67c1
Microsoft, what are you doing to address this issue? Secondly, what type of a QA Organization do you have that these issue are passing QA Testing and becoming Production Issues?