In my quest to get my motherboard (Gigabyte S-series GA-MA790FX-DS5) to wake-on-LAN, I tried upgrading the BIOS from Gigabyte’s download site from version F6 to version F8F. Bad idea! After the upgrade, the system would sometimes reboot spontaneously. This seemed to happen with more resource-intensive processes. The Gigabyte support folks were not really helpful (they just told me to check the cables), and, indeed, I am still working with them to fully enable the wake-on-LAN feature, which they claim is fully tested.

Since reverting the BIOS back to F6, the spontaneous reboot problems seem to have gone away.