I formatted my HDDs and made a clean Windows 8 install a few days ago. Now the system suddenly loses power at seemingly random intervals. (Instant reboot, no BSOD, no freezing)
I'd suspect the PSU, but it would be odd if a hardware failure happened just as I installed a new OS, and it hasn't failed under ~4 hour gaming stress, only while idle or I'm using a web browser.
The only thing I can find in the Event Viewer before the 41 Kernel-Power "The system has rebooted without cleanly shutting down first." -event is the following:
The description for Event ID 56 from source Application Popup cannot be found. Either the component that raises this event is not installed on your local computer or the installation is corrupted. You can install or repair the component on the local computer. If the event originated on another computer, the display information had to be saved with the event. The following information was included with the event: PCI 010101010101010100 the message resource is present but the message is not found in the string/message table
I installed the newest drivers to all the hardware: AsRock P67 Extreme4 (Chipset, Network), AMD HD6950 (Display), Xonar DG (Sound).
Other hardware includes i5 2500K, 120GB OCZ Agility 2 SSD and 2TB Spinpoint F3 HDD.
Everything seemed to work well while I was running Windows 7.