I've been experiencing some really bizarre issues with my desktop PC hibernating (and then sometimes bringing itself back up) at seemingly random intervals. The problem first presented itself this past spring while I was gaming online. It seems to occur most frequently while playing games, and almost never occurs when the PC is idling at the desktop, but there isn't really any one thing that I found I can do to induce the problem consistently. I've tried everything that I can think of to fix it, but the problem has persisted, and I still am not honestly sure whether this is a hardware or software issue.

I built my desktop myself about two years ago, and updated the GPU last November. Hardware components are as follows:
Asus P9X79 Pro motherboard
Intel i7 3820 CPU
Nvidia GTX 970 GPU
16 GB of RAM
Western digital 2 TB hard drive
Thermaltake case and power supply

The first thing that I did was to set the hibernation/sleep/turn off hard disk/turn off display power settings all to "never" within the "advanced power settings" dialog box, but this didn't fix anything.

My case has five case fans and a giant CPU heatsink/dual fan set up and is very clean inside, but just to be sure, I used a can of compressed air to blow out what little dust was there.

When I kept having issues, I wondered if I had somehow gotten a virus or a bad piece of malware, so the next thing I did was completely wipe the hard drive (filled it with zeros via DBAN on a bootable CD), reformat it, and then reinstall windows. Even with this clean install, I still experienced bizarre, random hibernation.

I still suspected that maybe somehow this was a software issue, so to try and rule that out, I actually installed a brand-new out-of-the-box Seagate 3 TB hard drive, but literally the first time that I tried to sign in after completing the Windows 8.1 installation, my PC randomly hibernated again.

At this point I started thinking that maybe this had to be a hardware issue, so I downloaded the Intel diagnostic software and even stress tested the CPU, but everything came back fine there. Next, I ran the Windows RAM checker/diagnostic, but that also reported no problems.

I called Asus, and per their recommendation, I unplugged the PC and removed the battery from the motherboard to try and reset it. I then flashed the bios to the most recent stable version available on their website. Still, I experienced the same issues.

I still am unsure whether or not the GPU might be contributing to the problem, but when my PC decides to cooperate, it can run Crysis 2 and GTA 5 at max settings at 1080p, 60fps for hours at times without issue. Sometimes though, the hibernation thing happens after playing a game for even a few minutes.

One thing that has been really confusing in terms of trying to figure out whether or not this is a hardware or software issue is that certain combinations of keystrokes sometimes cause the hibernation thing to happen. For instance, almost every time I hit "Alt + F4" (and recently "Ctrl Alt Del" as well...), it triggers the random hibernation.

Additionally, sometimes at the windows login screen when I am typing in my password, upon typing the last character of my correct password the system automatically hibernates and then brings itself back after a few minutes. Interestingly enough, I can randomly type and backspace as many characters as I like without incident, but the moment that I type in my correct password it triggers the hibernation craziness. This doesn't happen every single time, but has happened with increasing frequency lately, which is why I continue to wonder whether or not this really is a hardware or software problem.

As if this wasn't enough, my system has been extremely sluggish and not at all as snappy as it used to be when I first put it together. The onset of this noticeable slowness coincided with the hibernation issues begining back in the spring. I disabled every start up program through the task manager tab, and have defragmented the hard drive multiple times, but neither of these have really improved performance.

I am getting pretty desperate at this point, and I'm about ready to throw this thing out the window, so I would sincerely appreciate any possible insight as to how I go about fixing this.

Thanks so much and advance for all of your advice and support.