Question Trying to fix an old P9X79 LGA2011 system, need advice


Jun 12, 2010
Hi all,

I recently picked up a non-functional system from work with the idea that I could fix it up for my son's first PC.
I have built a few systems over the years, so I had some confidence I would be able to diagnose and repair whatever it is that has gone wrong. Well, it turns out I was a bit over-confident, but I am guessing someone on here has a bit more of a clue than me!

The machine specs:
  • Asus P9X79 mobo, LGA 2011
  • Intel Core i7 3930k
  • 8x8 GB RAM
  • GTX 560 GPU
The machine was built circa 2013 to serve as a scientific computing workstation. It worked fine until recently when it underwent a minor upgrade (SSD boot disk and OS upgrade). Shortly after the upgrade, it stopped working. Seeing as it is an old machine and there was no obvious faulty part to replace, it was decommissioned. I add this bit so it is understood that all parts are compatible and used to work fine.

Current diagnostics and issue description:
  • Power-on with CPU + Cooler fan only = one long, two short beeps (memory error) <-- I assume this correct and only add it here to show that the after-market speaker I plugged in is working and that the CPU at least seems to be passing the self-test. Also, whatever version the BIOS is, it worked till a month ago.
  • When I add some memory then the VGA status LED eventually goes red and stays red. There is no sound from the onboard speaker and nothing shows up on the screen. The same (red VGA status LED and no POST beeps) happens irrespective of whether the GPU is plugged in or not.
  • I have tested the GPU on my PC and it works fine.
  • CMOS has been reset by pulling and replacing the battery (6mins), no effect
Based on the above I assume either the motherboard or CPU has failed (with an outside possibility of memory being the culprit). My question on this board is the following: is there any way I can determine with reasonable certainty which component I need to replace?
I am leaning toward the motherboard probably because it is several hundred bucks cheaper than a replacement cpu, but I am afraid confirmation bias is pushing me the wrong way. There seem to be a lot of conflicting stories online, so any advice on how to isolate the problem would be much appreciated (by me and my son!).