K9N Neo-F, just over a week old and now won't boot.

Question

Having trouble with a new build using a MSI K9N Neo-F motherboard.  I suspect my Motherboard is faulty :( and plan on sending it back to Newegg for replacement unless someone has something else for me to try.  Here’s the original configuration:
MSI K9N Neo-F motherboard (MS-7260 Ver 1.0 w/ 1.3 BIOS)
AMD Athlon 64 X2 4600+ (65W – 2.4 GHz Windsor ADO4600CUBOX)
Gskill F2-6400CL4D-2GBPK (DDR2-800 4-4-4-12 @ 1.9~2.0V)
Gigabyte GV-NX76T256D-RH (GeForce 7600 GT) video card
Rosewill AP-500X (3.3V 30A, 5V 45A, 12V 22A)
NEC ND-3520A CD/DVD Burner
Seagate ST3320620AS SATA2 hard drive
For the first few days, everything appeared to work ok (though I had to leave the SATA 150 compatibility jumper on the hard drive in order for the motherboard to recognize it  ).  After day 3, it started locking up randomly (no blue screen) and restarting automatically, both while under high load and virtually no load at all.  Past day 5, it’s now to the point where it locks up even in the BIOS, and that’s only when I can get it to POST (otherwise, all I get is fan spinning and a blank screen, not even a beep).
The first thing I tried after day 5 was replacing the PSU with a Silverstone SST-ST56F 560 W PSU I have on hand for another build (this PSU is extremely well made and heavy by the way :smiley: ).  I figured this 560W monster could easily power the setup above, however the setup remained as unstable as ever.  I did notice in the BIOS while looking at the voltages before it locked up that the Vcore is jumping all over the place, from 1.240V to 1.372V!   I’ve built a fair share of A64 setups and never seen anything like this before.  It seems to point to a failure of a power regulator on the motherboard, just hope it didn’t damage my CPU as a result.
Next suspect was the memory, which I memtested overnight on another AM2 board and passed with no errors.  However, I read on a few other forums that the nVidia 550MCP chipset on the board doesn’t like RAM with a Tras under 15, so I swapped the RAM for another set of Gskill I had on hand (F2-6400CL5D-1GBNQ, DDR2-800 5-5-5-15 @ 1.8~1.9V) and reset the CMOS.  Unfortunately still no luck, it won’t POST half the time and when it does, it locks up less than a minute later while still in the BIOS.
My last shot was removing the 7600GT video card and replacing it with an old Matrox Milenium PCI one I had laying around.  My theory was not only to eliminate the video card from the list of suspects, but also the high power draw on the board that PCIe video cards tend to have.  However, it still fails to POST half the time.  Does anyone have any suggestions of things for me to try before sending back?  Thanks in advance.

Answer 1

Thanks for quick replies guys!  
Bosskiller - Yes, I tested both memory kits on another AM2 motherboard (Asus M2N) for ~24 hours each and both passed with no errors.  I tried setting the Vdim to 2.1 volts in the BIOS (while I was still able to get it to POST fully), but no luck.  However, since it's gotten very unstable and I reset the CMOS, the Vdim is probably back at the default 1.8 volts.  If I could just get it stable enough to make changes in the BIOS without it locking up, at least that would be an improvement. 
BAS - As mentioned, I tried using a Silverstone 560W PSU I had on hand with no luck either, that's when I noticed the big fluctuations in Vcore.  Speaking of which, are such fluctuation in the Vcore normal?  I've read several contradictor forum post on the topic and don't know if this is "normal" behavior for the k9n neo-f.
Thanks again in advance.