When it comes to my efforts to build an AMD based system, I'm pretty much back where I started.
Here's what I can reliably reproduce on my A8N-SLI:
Using a stick of ancient DDR ram (from a ca. 2003 box) IF I clear CMOS and cold-boot, bypassing bios setup (bios defaults loaded, F1 to continue), I can boot off of a floppy. I've successfully booted a Dos 6.22 floppy, tomsrtbt and memtest86+. Dos was perfectly happy (and quite fun to play with). Tomsrtbt worked fine for several hours, even with a system load of 2.00 via a dd of /dev/urandom into /dev/null. And memtest ran through four passes w/o error.
HOWEVER, a warm boot (C-A-DEL), would elicit the same hard lock right where I'd expect the BIOS logo to appear. For all purposes it seems to be hard locking during post. If I pull power to the system and turn it on cold, it boots fine.
This is the same behavior I would get if I used the crap-stick to boot into the bios and force the voltage and memory timings to 2.7V 2-3-3-6 which is the specs I found at the URL above. I can cold boot and run most anything from a floppy, but rebooting is a total loss.
Clearing CMOS works fine with the Corsair TWINX sticks in each of 512M, 1G and 2G configurations. Also I've been running one pair of those Corsair sticks in my older box (at DDR333 as it can't do 400) and memtest is happily churning away flawlessly. Booted windows just fine and so on.
Since it's not the power supply, not the memory, this leaves the mobo and/or the CPU. I now return to the store to return the perfectly fine, but useless to me power supply and pick up another A8N-SLI. I'm toying with the idea of simply switching mobos, but I have no idea what other mobo supports what I need: SLI, 4x DDR400, X2 939 and GigE.
I'll bring home the new mobo, swap it out and if it exhibits the same behavior I'll know that the problem must be the CPU, not the mobo, and so I get to deal with the hassles of returning a broken CPU. I'm praying it's not that, but since ALL of my problems are POST related and once I manage to boot everything is awesome, I think it's highly unlikely.
I'm hoping that the mobo is bad and the retail one will fix it (the first was mail order). My mail order supplier has a 30-day satisfaction guarantee on the mobo so I'll avail myself of that rather than try to return it as defective. Ironically the price has dropped 10% since I bought mine--not that they'd just credit me the difference or cover a swap with a new one.
Anyway, the quest continues.