RAM not showing up in post

I see that a great many people have this type of problem yet I've been unable to find a generic explanation of the factors that cause it.

My rig has 12GB ram (6 x 2GB G.SKILL 1600 DDR3). (rest of rig in sig). The whole 12 GB seemed to be recognized perfectly for the first dozen or so boots. Now only 10GB shows in POST and windows task manager but all 12GB is seen by CPUZ.

I suspect that some tweaks to things like QPI/DRAM voltage might fix it but I don't really know what I'm doing. Can anyone point to a guide to playing with RAM settings in BIOS and particularly what the safe voltage limits are?

I got this running stable but only 6GB of ram was recognized in POST..

Ai Overclock Tuner.....................[Manual]
CPU Ratio Setting......................[21.0]
Intel(r) SpeedStep(tm) Tech............[Disabled]
Xtreme Phase Full Power Mode...........[Enabled]
BCLK Frequency.........................[172]
PCIE Frequency.........................[100]
DRAM Frequency.........................[DDR3-1379MHz]
UCLK Frequency.........................[2758MHz]
QPI Link Data Rate.....................[Auto]

CPU Voltage Control....................[Manual]
CPU Voltage............................[1.15]
CPU PLL Voltage........................[1.80]
QPI/DRAM Core Voltage..................[1.20625]
IOH Voltage............................[1.14]
IOH PCIE Voltage.......................[1.50]
ICH Voltage............................[1.20]
ICH PCIE Voltage.......................[1.50]
DRAM Bus Voltage.......................[1.64]
DRAM DATA REF Voltage on CHA...........[Auto]
DRAM CTRL REF Voltage on CHA...........[Auto]
DRAM DATA REF Voltage on CHB...........[Auto]
DRAM CTRL REF Voltage on CHB...........[Auto]
DRAM DATA REF Voltage on CHC...........[Auto]
DRAM CTRL REF Voltage on CHC...........[Auto]

Load-Line Calibration..................[Enabled]
CPU Differential Amplitude.............[800mV]
CPU Clock Skew.........................[Delay 300ps]
CPU Spread Spectrum....................[Disabled]
IOH Clock Skew.........................[Auto]
PCIE Spread Spectrum...................[Disabled]

C1E Support............................[Disabled]
Hardware Prefetcher....................[Enabled]
Adjacent Cache Line Prefetch...........[Enabled]
Intel(r) Virtualization Tech...........[Disabled]
CPU TM Function........................[Enabled]
Execute Disable Bit....................[Enabled]
Intel(r) HT Technology.................[Enabled]
Active Processor Cores.................[All]
A20M...................................[Disabled]
Intel(r) SpeedStep(tm) Tech............[Disabled]
Intel(r) C-STATE Tech..................[Disabled]

Now I'm back to default stock settings and only 10GB is detected.
Can anyone give any pointers or link to a guide?

thanks

Edit: Problem solved see here http://www.overclock.net/intel-memor...ml#post9075853
Edited by paleblue - 4/16/10 at 8:06pm

@Wishmaker thanks, Iill try that as soon as I have some time. Funny thing is it's so random, sometimes I get 6Gb, somethimes 8GB, sometimes 10GB. Doesn't want to give me 12GB ever now. I'll test each stick but it has to be bios settings surely.

@Hexa Thanks mate, so many people seem to have a similar problem I hope I can solve it with BIOS settings and post the solution here for others to see.

"Test each stick by itself in every slot to assure all slots work" will do later

"Go to msconfic and make sure maximum memory is unchecked." ??? don't understand this

As for the BIOS settings, I'm uncomfortable raising voltages without knowing what the safe range of values are.

My heatsink is a Corsair H50 and the screws are tightened all the way down. The temps are fine so it's seated well - can excess pressure on the cpu cause this really?

I only just built and installed this box 2 days ago so I don't think it's windows.

Thanks for your help, I will try testing the RAM but I would appreciate more guidance on bios ram voltages before I start increasing things.

I don't believe it.

I spent an hour testing my 6 RAM sticks one at a time and then in varying configurations with all bios settings at stock. When testing just 3 sticks at a time there was a configuration that only showed 4GB but but I ignored that because moving them around I finally got 12 GB to be recognized consistently.

I'd heard that sometimes certain sticks like to be in certain slots so I didn't worry too much.

So all was good (note the word "was"). Ten or twenty reboots later 12GB showing up in POST without fail.

So, I decided to try overclocking again, gently at first I used the "Getting Started And Overclocking to 3360MHz" guide from this page:

http://www.clunk.org.uk/forums/overc...beginners.html

and BINGO I had 3.3GHz running great with nice cool temps passing prime95 and LinX perfectly and with the full 12 GB RAM detected. (I had manually set the RAM timings of 9-9-9-24 for my RAM (that's what's printed on the sticker on the sticks)

So buoyed with enthusiasm thinking I had it sussed I moved on. I tried the next setting for 3.8GHz (from that same page as above) and guess what, POST only sees 4GB of RAM. Tried a couple of reboots still only 4GB showing up. So I reset the BIOS to default settings and STILL only 4GB showing.

Powered off, resat each stick of RAM, now 8GB showing. And this at stock speeds everything reset to defaults.

I'm going crazy here. What shall I do next?

It was left set to auto as per the guide on that page I linked. Do you have any suggestion?

Update: I removed all the ram and messed around swapping the sticks about until 12GB was recognized. Now I'm back to 3.3GHz with all 12GB showing like I was before. I'm about to try 3.8 using the mainly auto settings in that guide but I expect it to play up again. The annoying thing is my temps are fine, ran prime95 overnight on blend at 3.3 and no probs at all, max temps 60,59,60,57.

I know I can get higher but for this RAM issue. Do I need to be RMA'ing RAM or mobo or are these problems normal?