I am glad to see I am not alone with this issue.

Windows Kernel event ID 41 error "The system has rebooted without cleanly shutting down first" in Windows 8.

http://support.microsoft.com/kb/2028504

This issue recently started on my game rig, and I cannot for the life of me figure out what could be causing it. I strictly monitor my temps. During gaming my CPU cores run 41-50 degrees Celsius. My GTX670s in SLI run 70 degrees Celsius or less, and I am running a Corsair HX1000W power supply, so power is not the issue.

So far this has happened two times, once on 8/27/2013, then again last night, 9/4/2013. On 8/27 my system totally shutdown and rebooted. Last night, my system just froze; everything was still on, just frozen in a still-screen, and I had to hold the power button down to reboot the machine. No BSOD at all, just what I described above.

Both times I was playing FFXIV: ARR. I built this rig almost a year ago, and game daily on it with no issues until recently.

The only things that are recently different are:
1. Instead of playing Rift, I am now playing FFXIV: ARR
2. I am running several monitoring programs, such as MultiPing, Argus Monitor (paid version), HWMonitorPro (paid version), RealTemp 3.70, Moo0 System Monitor, and Rainmeter.
3. I installed BitDefender 2013 Total Security in lieu of the built in Windows Defender that comes with Windows 8.

My Windows System and Application event logs are totally clean. I have been constantly checking them, with the exception of the Event 41.

I am currently running the NVidia 320.49 drivers.

Here are my game rig specs:
Case: AZZA Hurrican 2000
Mobo: ASRock Extreme6 Z77 LGA1155
CPU: Intel Core i7-3770K Ivy Bridge 3.5 GHz 8MB cache LGA1155 (BX80637I73770K)
CPU cooling: Corsair Hydro H80 high performance liquid CPU cooler (CWCH80)
RAM: Corsair Vengeance 16GB (2x8GB) DDR3 1600 MHz (PC3 12800) (CMZ16GX3M2A1600C10)
Over clocked: none
HD1: Corsair Neutron GTX 240GB SSD
HD2: SATA 2.0 Western Digital Green, 1TB
Raid: none
OS: Windows 8 Professional
Video card 1: EVGA GTX670 2GB
Video card 2: EVGA GTX670 2GB
SLI: Yes
Monitor 1: 28" Hanns G HZ281HPB LCD
Monitor 2: Viewsonic VA2703 27 inch Full HD 1080p Widescreen LCD Monitor
Sound: Onboard RealTek 7.1 surround
Power supply: Corsair HX1000W
UPS: CyberPower Intelligent LCD Series GreenPower UPS CP1500AVRLCD 1500VA 900W
Keyboard: Logitech G510
Mouse: Logitech G600 MMO gaming mouse
Headphones: Logitech G930 wireless gaming headset