12gb of ram installed, only see's 4gb or 2gb

Welcome to Tom's Forums!  

10GB loss beats the 8GB record I've seen.

Q - Is your Vista 32-bit or 64-bit?
Q - What exact XMS do you have installed? CMX12GX3M3A2000C9 or CMX12GX3M3A1333C9...

R3F {R3E} http://www2.corsair.com/configurator/product_results.as...

Windows 7 Ultimate 64-bit

2x CORSAIR XMS3 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Triple Channel Kit Desktop Memory Model TR3X6G1333C9

They're not XMP, so you'll need to manually set the RAM. If the following fails then BIOS 0505 might be an option, but first things first. I assume that the 2 sets are NOT randomly mixed together; Set 1 = A1/B1/C1 and Set 2 = A2/B2/C2.

1333 MHz 9-9-9-24-2T @ 1.5v

BIOS:
Load Defaults **
** if you changed CPU Fan {e.g. 100% Corsair H50/H70} or IDE-> ACHI then change from defaults.
AI Overclocker Tuner -> Auto
DRAM Frequency -> DDR3-1333 MHz
DRAM Timing Control {enter}
-> 9-9-9-24
Timing Mode 1N -> 2N
--
* DRAM Bus Voltage -> 1.5v~1.6v
* QPI/DRAM Voltage -> 1.20~1.35v in 0.05 increments

* {this is sometimes needed for 6 DIMM} if there's not enough voltage the DIMMs will be under powered and hence the irregularities.

Failure, pull Set 2 A2/B2/C2; remove black slots -> see if 6GB shows-up. Next, swap Set 1 for Set 2 in the Red slots -> see if 6GB shows-up.

Post those results. If BOTH single sets work then it's a Voltage issue.

Failure, use the settings above, create a Memstest CD/DVD {ISO/zip} http://www.memtest.org/

Yes I am using a Corsair H70, forgot to mention that.

Then I assume that you set the fan @ 100% a/k/a pump.

BIOS:
CPU Q-Fan Control -> Enabled
CPU Fan Profile -> Turbo

Q - Did the other BIOS settings correct the problem?

About to try now. Let you know!  

It worked, computer recognizes all ram installed!

Cool Glad to hear!  

Use the Fan settings for the H70, you want the pump with 100% power + runs cooler.

Alright! Thanks a lot for the help.

What if I overclock my CPU, it usually changes some of the RAM parameters. Will I be ok?

If you used XMP and didn't manually set the voltages then yes, but it's always a good idea to double check DRAM Frequencies. The manual settings lock-in the values which is one of the reasons I prefer to manually set all the RAM values.

Well I just got home from work and check it... its reading 2gb of ram  

Sorry to hear, 50/50 {bad stick/voltage} per above. Just 'in case' use Isopropyl alcohol and dampen the RAM contacts then place in DIMM slots clean and repeat X2 per DIMM, allow to dry ~10 minutes. In the machining process oils are used so not to tear the DIMM contacts while Mfg.

My assumption is the RAM is good, but the contacts/voltage isn't Dialed-in yet.

Failure:
1: Try the upper values (1.55+v/1.30+v)
* DRAM Bus Voltage -> 1.5v~1.6v
* QPI/DRAM Voltage -> 1.20~1.35v in 0.05 increments

FULLY using ALL DIMM slots takes more power and all too often ALL the DIMM slots do not 'get' adequate power, therefore requiring a slight over voltage. None of the voltages I'm posting are 'high' and I am on the conservative end. RAM can run ±0.2v~±0.3 Volts and is considered within normal ranges. Think of it with 6 filled slots as having a runt of the litter not getting enough 'juice.' Too much or too little - neither is good, you need to keep 'tweaking'.

Some people might recommend, but I know Volts = Heat.
* DRAM Bus Voltage -> 1.6v+
* QPI/DRAM Voltage -> 1.3~1.4v in 0.05 increments

2: Failure with upper values.
Failure, use the settings above, create a Memstest CD/DVD {ISO/zip} http://www.memtest.org/

I'll keep up with you in this post.