1000HX - POST restarts causing bios corruption?

Greetings,

I've been having a randomly repeating issue ever since I designed and built my current system a year or so ago. Basically, every once in a while, when I first turn the system on it will begin powering up for maybe 5 seconds, then turn itself off. A few seconds after that, it will turn on again and, generally speaking, then continue normally through boot and into windows.

I've checked the cabling inside the case a few times to make sure everything is secure, as well as checking to make sure the power switch is wired correctly to the front panel section of the motherboard, but I've been unable to locate a problem. Once I get into windows, I've never had a single problem - no random restarts, freezes, or crashes despite heavy bleeding-edge gaming, raytracing using all 6 cores/12 threads, and so on. The system is basically rock stable after POST, runs very cool (generally below 40 celsius idling and never above 60 even with all cores at full bore), and all voltage levels have always looked fine, so I've kind of ignored this problem up until now.

More recently, however, things seem to have deteriorated a bit and I'm trying to figure out the best way to proceed. A week or two ago, after I pressed the power button it did one of the power down/turn back on things I mentioned above, but instead of proceeding normally, the system turned off again, then back on. Then again.

So it did this three times in a row before letting me far enough to actually see anything on the screen and this time, I got a message from the Gigabyte motherboard that the primary bios was corrupted and that it was being restored from the backup (fortunately many of their motherboards have a dual-bios setup). After that the restoration, I got back into windows normally.

I figured, okay, maybe this was a fluke - I updated the bios to the latest version (FE, I believe) and proceeded as normal. Then a couple days later, turning on the system immediately produced the corrupt bios thing again and another restoration. I got into windows fine after that, but now I'm worried.

The real issue here is whether the problem is the motherboard, the power supply, or something else entirely (though I doubt that).

I guess my first question is this: if this was, say, the power supply, could a bunch of restarts in a row as the system is POSTing corrupt the bios and cause the restorations I'm seeing?

Or is it simply that the motherboard is screwed up in some way, which is corrupting the bios, which causes these power off and on episodes when the system is turned on?

Any help would be appreciated and I'll provide any other info you might need.