You have been thorough, and that's good.
I have to start from basics, so please run Memtest 86+ (per instructions above) on each stick of RAM you have.
Next, please run Seatools for DOS on your hard drive, instructions below. I noticed that in your perfmon file, only the SMART feature was tested; the Seatools utility goes a lot deeper than that and can find problems that have not tripped SMART yet.
Go here and download Seatools For DOS (free)
> Accept the EULA and download the ISO file.
> When download is complete burn the ISO to a CD or DVD.
> Disconnect any other hard drives in your computer (not optical drives) leaving only your problem drive connected.
> Make sure your BIOS is set to: 1st Boot Device = CD drive, 2nd Boot Device = Hard Drive.
> Insert the CD in your optical drive and reboot.
> When the program opens, click the upper left corner for the Long Test.
> Note: if you get a pop-up window telling you that SMART has tripped and asking if you want to continue, choose Yes. Be sure to post that in your next reply along with the result of the test.
At the end of the test, you will get either a Pass or Fail notice. Post the result in your next reply.
Be sure to have your hard drive directly installed internally to the motherboard, not in an external case.
> I will assume that you have reset your CMOS (BIOS) back to factory default; if not, try doing that.
> Have you checked what your CPU temperature is running at? Shutdown can happen if it overheats. In addition, check the overheating shutdown setting in the BIOS; if it is set too low, it may be shutting down at too low a temperature. A long shot, but it's easy to check out. Also check out your "Cool & Quite" feature, if your BIOS has that.
Have you checked your power and reset buttons? I have seen them begin to fail and cause random problems, and are easy to check. In case you aren't sure, following is my canned tutorial:
> Power your unit down.
> Leave it plugged in.
> Pop off the side of your computer, and trace the small cable running from your front panel, on/off power switch to where it plugs into the tiny socket on the mainboard. Gently pull that plug off, revealing two contacts.
Take a flat-bladed screwdriver, and short the two contacts. Your computer should immediately power up and boot normally. If it does not, your power switch is bad. However, in your case, I expect that it will boot normally, so run the unit normally for a length of time to see if the problem ceases.
Repeat this for your reset button also. I have seen them go bad and cause auto-reboot problems, but not as often.
If no good result on any of the above, replace your connection cables 1x1 to make sure the are not shorting.
If STILL no joy, you can start checking for software conflicts in the system, which are a pretty common problem. I suggest starting as follows:
> Boot into Safe Mode and run the system 24/7. If your shutdowns cease, at least you know that it is one of the programs or drivers running that is causing it.
> Run a clean boot from the msconfig command window; if your problems cease, it is a system conflict. If you aren't sure how to do this, HERE is a tutorial.