Finding the cause of total hardware lock-ups

Question

The new build has been running reasonably well, and I've done no major optimizing so far, and no overclocking (yet). However, I've been having infrequent and seemingly random system lock-ups that would appear to be hardware related.
Last night was about the fourth or fifth of these. I had been working on and off throughout the day on a 4-camera multicamera project, and having no issues at all. This was a TOTALLY different multicam experience than I've had with CS4, where MC was hardly usable. Anyway, I was going to make my last few edits of the night when the system locked up--I had just started playing back a sequence when it happened. No hard drive activity, no keyboard/mouse interaction, no bluescreen--the audio that had started playback, however, got caught in a short loop and made an annoying racket. The only way to return to normal was to hard reboot with the power button depressed. No error or fault is logged in the Windows event logs, beyond the reboot which is recorded as something like, "Your system restarted, probably due to you turning it off... don't do that." The actually fault that perpetuates such a drastic action is not recorded. My initial thoughts were that the RAM has a bad chip somewhere, so I've run a memory test for over 8 hours now, and had 0 errors reported. There were no lock-ups, either--the system has been just humming along that whole time. This obviously does not rule out the RAM, but doesn't make it easy to say it's the problem, either. The only "tweak" I've made to the system is the RAM, and that's by setting the DRAM frequency to 1600MHz; nothing else has been altered in the BIOS.
The last two lock-ups occured in one day, when I was attempting to export to an H.264 file, through the AME queue, with hardware MPE enabled. At different points in the export, the system locked, with similar results as above. After the second lock-up, I disabled GPU acceleration in PPro, and the export completed just fine. Interesting, I thought. However, I'd done other hardware MPE-assisted exports earlier that day and in previous days, with no lock-ups.
As mentioned, I'd encountered at least one other hard freeze, and if I remember correctly, I was in Premiere but not doing anything. I'd walked away from the system for a little while, came back, and it was Living Dead on my return. I hadn't been rendering, importing, playing back, or anything else.
I've been checking my temps with HWmonitor, and there isn't anything out of the ordinary as far as I'm aware. I'm really not stressing the system much, pretty basic and rudimentary edits. The memory test has now done about 600% coverage, and no errors. The bizarre coincidence is that these lock-ups occur when I'm in one of the Adobe programs--but I've never seen software cause a lock-up such as this before.
So... where do I go from here? The lock-ups seem to completely happen at random, with no particular instigation. Is there some sort of other monitor software I can run in the background that might indicate hardware failures that Windows is not able to catch?
I'm hoping you hardware gurus can shed some light on this bizarre predicament... thanks in advance for your insight.
ADDENDUM:
It would seem to make sense to post my hardware... duh:
ASUS P6X58D
i7-930
OCZ  Gold 12GB (6 x 2GB) DDR3 1600 (PC3 12800)
GIGABYTE GeForce GTX  480
COOLER MASTER HAF 932
COOLER MASTER Silent Pro 1000W
Western  Digital VelociRaptor 150GB (system drive)
HITACHI 500GB 7200  RPM SATA 3.0Gb/s
4x SAMSUNG Spinpoint F3 1TB  7200 RPM SATA 3.0Gb/s (running RAID 5 with onboard controller)
Noctua NH-D14 CPU Cooler

Answer 1

Well, I really wanted Jeff's suggestion to be the solution, but alas, troubles remain. And it would appear that something far more sinister is happening than flaky codecs or software.
The good news is that I can now reliably repeat the lock-up, each and every time. The bad news is that the lock-up occurs whenever I attempt an export. I'm trying to get a 75-minute multicamera edit onto a DVD, and the moment the actual encode begins, the system goes into a hard hang. I have a number of audio clips that are being used, and I see "Adobe Premiere Pro is preparing audio for export" or something like that, and then once the video processing begins, it's curtains.
At first, I thought it was something with the hardware MPE--I'm using a GTX 480 with the hack. Editing works well--remarkably well. Encoding is a different issue, altogether, and it doesnt' matter whether I start the export with the Queue button or the Export button. I tried disabling GPU acceleration, and at first, I thought I had solved the mystery--the encode actually began and progressed for about 30 seconds. However, inevitably it would seem, I got the same hard hang.
The first couple "hangs" were actually system restarts; the Windows desktop would disappear, and moments later, I was back at POST. I then disabled the "Automatically restart" option in Windows, and after doing that, I simply ended up with a frozen system and desktop. I'm not sure those are coincidental, actually; I'm going to test that again this morning to see if I get the restart or the hang.
I've been checking out my temperatures with HWMonitor, and as far as I can tell, I'm not going off the charts with temperatures. Temperatures do climb (I have HWMonitor as I start the encode) for both the CPU cores and GPU, but nothing drastic, and there is no way that it's getting too hot in the 5 seconds that the encode is running before the hang. What about the power supply? I can see wattages for the CPU fluctuating drastically as the encode tries to begin, which I would gather is SOP for the operation of a computer, but is it possible that I am getting too much/too little juice? I've got a 1000W Cooler Master PSU, the components you see listed above, and 6 hard drives--this would seem to be more than sufficient to me (for my current use), but undoubtedly, the system is pulling more watts as it starts to work harder. Unfortunately, there is nothing I can really disconnect to test this theory, since I need all of the components and hard drives connected to do anything.
I'm at a total loss, guys, and I'm more than a little frustrated because I've got a pretty expensive paperweight sitting in my office. Unfortunately, I live in a pretty rural area, so finding a trustworthy computer tech locally is a challenge, so I'm hoping that you tech-savvy folks can through out some places to look.
Help me, Obi-Wan Kenobi... you're my only hope...
Thanks, all...