Thanks Arne. My 2nd bios is still an old version, pre IB-e, so I can't switch it unless I flash it to a new image, which I'm a bit reluctant to do while the system is acting weird (a failed bios flash and a borked mobo is the last thing I need).

It does seem almost like what you'd see with a bad ram oc, except that my ram was working 100% fine last night when I shut down -- I wasn't even doing anything interesting with my system, just typical websurfing etc. It doesnt seem there should be any reason for a hardware failure this morning. 😞

Yeah well these things often do go with no warning if that's what it is...the reason you might try one stick of RAM at a time see if anything changes. OK I hear you on the BIOS ....you could try re-flashing the BIOS you are on then with a fresh file....BIOS flashback.

You could disconnect the battery and PSU for an hour or so even overnight if you can....totally reset the board...

When you say power button you mean the one on the board itself...if a case button remove Qconnector from board and try board power button.

So, since my last post I fell asleep watching TV, and when I woke up from my nap and tried one more time to start my system, it magically started up as if nothing were ever wrong with it in the first place.

I swear there are gremlins living inside this computer whose whole purpose in life is to confuse and irritate me. lol
___________
*edit: after getting back into Windows, I notice that the time is wrong. A quick "update from internet" sets it right again, but much like the last case of "gremlins" struck (this isn't the first time the system has inexplicably refused to post for an extended period and then magically just "worked" again out of the blue), I'm willing to bet the system time in bios is wrong, too, and it's the mismatch between the timestamps that is causing the system to fail to post. Is there anything in particular that would cause the cmos timestamp to go out of sync?

Aw chrisnyc I'm sorry to say you did in fact fall asleep in front of the TV but you haven't woken up yet....you're just dreaming the problem is fixed...and this reply is just your sub-subconcience trying to get you to wake up.....WAKE UP CHRIS!

I would have a look at replacing the CMOS battery? Have seen this behaviour once or twice before.

Thanks HiViz, I'll switch it out just to be on the safe side. p.s. I checked the time in the bios and it was correct. No clue why the Windows time suddenly went out of sync or if that could cause a problem with post?

Oddly, it happened again yesterday after attempting to wake the system from sleep mode (which I rarely use). That time a quick cmos reset fixed the problem. The more perplexing case is when it happens and cmos reset doesn't fix the problem, which has happened twice now. Both times the system flat out refused to post for hours/days, then just suddenly worked again as if by magic.

I still blame the gremlins. 😉

Just a little follow-up on this one, in case my diagnosis/resolution helps somebody else who may come across this thread....

It turns out the problem is a faulty heatsink in my psu which causes the power supply to randomly shut down and/or refuse to power on. I pretty much ruled out the psu in my troubleshooting because my psu is literally brand new, purchased new less than 2 months ago, and it's a very reputable model. BUT, turns out EVGA just issued a recall on several models of their power supplies for this exact problem:

http://www.evga.com/articles/00803/

So, RMA is in-progress, and fortunately EVGA cross-ships, so the only down time I'll have is any that is due to the hardware malfunction (typing this on my laptop right now b/c my pc flat out refuses to power on....again).

At least it's not the mobo as I suspected. Pulling out the psu to RMA is a lot easier than disassembling the entire system to pull out the mobo. 🙂