Crosshair II Formula + Dominator 4GB - only sees 2557MB?? [SOLVED]

Hey folks. I finished putting together a system recently and all was well for a while. I've got a Phenom 9950 Black, Asus Crosshair II formula board, and 2 sticks of 2GB Corsair Dominator PC2-8500 memory. The build went alright, I put vista ultimate on it, etc. and everything ran fine. Then I noticed that my idle memory usage hovered around 45%. In the bios, on the main screen, it reports:

Installed Memory: 4096MB
Usable Memory: 2557MB

And consqeuently I'm only able to use around half of my memory. Yes, I'm running vista 64, and both windows and linux see that same amount - 2557.

My question is, why the **** am I only able to use 2557MB? I disabled memory remapping and the onboard GPU, and I could have sworn that that "installed" number was 4095MB when I set this thing up. I disabled all overclocking features and ran memtest twice on each individual stick, then on both installed; all passed. Any clues guys? If I run only one stick, I can most definitely use all of it.

maybe your OS is reserving a chunk of it

Well, a CMOS clear fixed it; kinda feel stupid that i didn't try that earlier. Wish i knew what caused it tho.

Thanks for the suggestions.

edit: I since found that enabling "memory remapping" allows me access to the rest.

Yeah, it's pretty sweet. That board's got other problems for me though; I can't overclock, for instance http://img.tomshardware.com/forum/ [...] s/pfff.gif The moment I try to change the multiplier, it won't post (hangs at "DET DRAM" )

I'm running BIOS version 1101


Here are my Extreme Tweaker Settings, leave on Auto if a change is not referenced.

AI = Manual
CPU Freq = 200
CPU Multi = 16X
K8 NB HT Speed = 2Ghz
K8 NB HT Width = 16 16
PCI-E = 100
CPU-NB Multi = 10X
Vcore = 1.4250v
DDR2 V = 2.100v

_______________________________________
DRAM Configuration

Memory Clock Freq = DDR2 1066
Tcl = 5
Trcd = 5
Trp = 5
Tras = 15
1T/2T = 2T
Gang = Enabled
Remapp = Enabled
Skew = Auto

I'm responding to this on exactly those settings!

However I'm air cooling you're water cooling, which means you're running cooler than I am anyway or you should be!

You'll have to go the trial and error route and find your settings that work for you, for example since you're essentially running cooler you may be able to run a 16x multiplier at 1.400v core or 1.375v, so I'd suggest starting out to set your Vcore on auto and try 14X and see if you can boot into Windows and run 3Dmark03 successfully, if you can then set the Multi to 15x and repeat the test, up to 16X and beyond if you're water cooling you should or could reach a 17x multi, if any tests don't complete increase the Vcore a notch at a time and try again until you find the voltages you can run each multiplier at.

My Specs are;
CPU AMD X4 9950 BE w Zalman 9700
Corsair Dominator 2X4096-8500C5D
2 BFG 8800GT in SLI
Silverstone OP-1000W P/S
Seagate SATAII 500G HDD
ASUS Crosshair II Formula M/B
Creative Xtreme Gamer Fatal!ty Pro Soundcard