[Solved] Bad motherboard? Need help with diagnosis

I built my first rig this past summer. I've had everything running like a dream for almost 6 months now, but yesterday the whole thing crashed. I was running a game one moment, and the next moment the entire system had shut down. No funny noises or smells, and no beeps or error messages. After some poking around I think the problem is in the motherboard, but because I'm fairly new to the scene I'm not entirely confident in my ability to diagnose the problem. I'm hoping somebody here can help me. Here are my vitals:

MB: ASUS P8H67-M LE
CPU: Intel Core i5-2500K
RAM: (2x4GB) 1333 by Crucial
PSU: Thermaltake Toughpower XT TPX-775M

My first suspect was the PSU, because the failure looked and sounded like the power got interrupted. But this PSU is designed to keep running for a few seconds after the power switch is hit, which is exactly what it did. It seems to be running as intended, and the "Standby" LED on the side of the PSU indicates it's functioning normally. What's more, when I press the power button on my case, all of the fans turn on for a split second: PSU fan, case fans, CPU fan, and graphics card fan. But immediately they all shut off again, and the PSU does its few second cool down cycle again. (Interestingly, this only happens if I've just cycled power to my surge protector. Any subsequent presses on the power button produce no results at all unless I cycle power to the surge protector again.)

All this make me think the PSU is not at fault, which leaves me with only a few options. I currently have all my peripherals unplugged from the motherboard, leaving only the CPU and RAM connected. That changed nothing, which means it has to be with the motherboard, processor, or RAM. I've tried reseating the RAM and rearranging the sticks in every possible combination (including taking one stick out), but that also produced no change. Also, the motherboard has an LED that's supposed to light up when it detects a problem with the RAM, and it's off.

So if I'm right, that leaves me with only the MB or the CPU as the faulty component. I don't know how to proceed from here, other than I've heard that CPU failures (especially new ones) are much rarer than motherboard failures. So I'm left with the assumption that the MB is to blame.

Can somebody tell me if my assumption sounds right, or if there's something I've missed or still need to test? I can't offer money, only my eternal gratitude.

It still sounds like a PSU problem. I'm much more inclined to trust ASUS over Thermaltake. Do you have a spare quality one or one you can borrow from a friend to test on your system?

Glad you found the problem. Keep us posted if anything else comes up

This topic has been closed by Mousemonkey