PC boots, shuts down after a couple minutes with memOK light solid

innocuous_name

Prominent
Jun 14, 2017
2
0
510
This build is about a year old, it has just started this behavior. It boots, but only lasts for a couple of minutes. It will boot to windows, or just to bios, and just the same after about 2-3 minutes is shuts down. I initially thought the CPU must be overheating, but when I went opened the case to troubleshoot, I notice it's the memOK led that's on.
I've juggled the memory sticks, in various slots, and the behavior is always the same.
So I'm narrowing in on a Motherboard issue, but then I wonder what would be failing on the mobo to cause it to fail in that way? I hate to go through a mobo replacement for that not to be the culprit.
(Additionally, there is a graphics card in play as the mobo doesn't have any video out, but I pulled out the graphics card and booted it to bios, let it sit for a few minutes and it died, memOK again.)
Any thoughts?
mobo: Asus M5A99FX PRO R2.0
ram: gskill 2x4MB sticks
cpu: AMD FX8350 8core
 

innocuous_name

Prominent
Jun 14, 2017
2
0
510
Well, I bought a new motherboard and rebuilt the machine today, it all worked great for about 20 minutes then did it again. This mobo doesn't have the memOK light, so can't say that's it, but I'm pulling my hair out :|