Odd Ram Issue

Has anyone experienced this issue. A family member was having a issue with windows not posting every time from a cold boot. He would hit restart and then the computer would post the second time. When I first looked at this system it seemed to running ok. So I first downloaded a few programs CPUZ , HWMonitor and Prime 95. I did notice from CPUZ that the ram was running 1600mhz.
System Specs:
Asus Sabertooth 990fx
Amd 8320
GSkill Ripjaw X DDR3 ( 2X4gb ) 1866
Corsair AX 750w
Corsair H100I ( 4 fans in push/pull )
HAF 932
Again after seeing that it was running at 1600MHz I checked bios and everything is stock and set auto. I manually set the ram to 1866MHz , Save and restart. The system would not post. I cleared Cmos and tried again, still would not post. I then put the ram back to 1600MHz and system restarted fine. I then just wanted to see if the system was stable and ran Prime 95 for 1 hour with not errors or dropped cores all temps were fine.
I then ran windows memory tool, the computer shutdown before finishing. This pointed to memory issues. I have not at this time removed all but one stick and run memtest 86 an each stick. That will be my next step. I am just wondering if this maybe a deeper issue than just the ram, ( Motherboard or CPU ). Was just wondering if this has happened to anyone else and found out it was not the ram causing the problem. I would also add this system is only 6 months old and new OEM Windows 7 pro.
Thanks
jshake

A bit late but here goes. Usually the MB has bad caps. Also, could be PS.

I might suggest bumping up the CPU_NB voltage and see if that straightens it out. Not all the FX have great IMCs.

Seen this with an Intel without CPU load line calibration.(cold boot POST failure) (with my Asus P5QL Pro and Core 2 Duo E4500, IIRC)
Enabling CPU load line calibration solved the problem.

Could be RAM timings messed up as well, did you set to XMP?