Alright, after a significant amount of testing (and buying a boatload of parts) I am pretty sure it is the motherboard. I rigged up a system speaker using an old motherboard 4 pin connector and hooked it up to a small speaker I bought at Radioshack. The only emitted sound (assuming it works) is one continuous beep. According to the BIOS beep codes from ASUS's website regarding the M4A78T-E, this means a power failure.
I attempted this after removing the motherboard from the case, along with the power supply, and placing both solely on a large piece of cardboard, as per your awesome instructions. Hooked up only 1 stick of RAM (but tried each one individually), the 24-pin and 4-pin power connectors and a DVI cable via the onboard graphics. Tried this with my current Corsair PSU, and an older, but known to work 650w PSU from another computer. On both occasions, the CPU fan spins up, but nothing else. Tried clearing the CMOS one more time, to be sure, which led to the same result.
I am somewhat surprised my ASUS board has gone bad after about a year (assuming I am correct) but I would have been down right shocked if it was my TX750w instead. Thank you for all your epic help, I really appreciate it, and I will be RMA'ing this board as soon as possible.
The only lingering concern I have is I let the system run for about 3-5 minutes, and pulled the heatsink to see if there was a change in temp, and as far as I could tell there was not. Not sure if this is indicative of the CPU going bad, or power to the CPU not being there.
One additional note: I reseated the cpu with a new heatsink/fan on the off chance it was overheating, or had come loose. I have never noticed any extraordinarily high temperatures, even with the fourth core unlocked, but at the same juncture...you never know. Also, I pulled the CPU, just in case I would get a different beep, or series of beeps, and nothing but the same continuous tone.
If you have any further advice, or can think of an alternative possibility, I would love to hear it as I will be supremely disappointed if I get the motherboard replaced, and it turns out it's not the culprit.
UPDATE: (and feel free to e-slap me for this one) With my finger on the power switch of the alternative PSU, I powered on the mobo with a single stick of RAM and the CPU (no heatsink!) and flipped the switch after about 5-10 seconds. There was a definite change in temperature on the CPU.
SECOND UPDATE: Since I am not the patient type when it comes to my hardware not working, I ordered this: Motherboard
pending any issue's anyone see's fit to raise.
Edited by StewBizzle, 29 December 2010 - 12:37 AM.