This is happening to me now too. I have a Samsung Ativ Tab 3 tablet, which has been running Windows 8.1 flawlessly forever. Yesterday I ran windows update (it had been a couple of months since last updating) and received a number of updates. While applying
the updates, I got the Shutting Down message, and the tablet shuts down.
Now, every time I start it up, it lasts through the login, and just as it gets to the desktop, it shuts down.
I can boot into Safe Mode without issue.
So last night, I did a full wipe and reload - back to Windows 8. I installed Windows 8, no problems. Added all the Windows 8 updates, no problems. Upgraded to Windows 8.1 through the store, no problems. Applied all the Windows 8.1 updates.... and, boom,
I have the shut down behavior again.
I'm going to reload again, and ignore that update, and hope it helps.
THANK YOU!
Glen