RAM is not being detected, even though it was before?

I bought some Corsair 6GB (3x2GB) DDR3 1600MHz XMS3 Memory for a completely new system back in December. This worked perfectly up until a month or so ago where I noticed my PC is only detecting 4Gb of RAM. There were no error messages or anything. My BIOS only displays 4Gb too, but when using CPU-Z, it says I have 6Gb installed and shows the SPDs for all three slots perfectly. I have swapped my RAM around too and have identified the potentialy corrupt stick.

I have tried Memtest and it also displays all the slots but still only detects 4Gb of RAM. Memtest displayed no errors after 16 passes.

What should I do? Is there anyway to fix this?

Attached is a screen-shot of CPU-Z and Task Manager. The SPD for all three slots of memory read identical to each other.

Hardware:
Asus Sabertooth X58 Socket 1366 ATX Motherboard
Intel i7 930 2.8GHz Socket 1366 8MB L3
Corsair 6GB (3x2GB) DDR3 1600MHz XMS3 Memory Kit CL9(9-9-9-24) 1.65V
Asus HD 5850 DirectCU 1GB GDDR5 DVI HDMI Display Port Out PCI-E Graphics Card
Antec TruePower New 650W Modular PSU

Thank you for your help.

 

what os are you running?
looks like there are 3 separate banks of memory. 2 slots in each bank with a total of 6 slots.
do you have them installed where each bank has a memory stick?
according to the manual it should be installed in A1 B1 and C1. those slots might be the same color.



you might want to try testing out each stick one at a time in slot A1 and run memtest on each stick.