Where did my memory go?????

I have a small problem. It seems I have lost a gig of memory somehow!

Here's my rig;
CPU: QX6850 Quad Core Extreme 3.0GHz
Cooler: Zalman 9700 Ultra Blue LED
MB: ASUS Rampage Formula X48
Ram: 4GB Crucial Ballastic Tracer PC2-8500 DDR2 1066Mhz (4X1GB)
VGA: VisionTek HD 3870 512MB GDDR4 Overclocked Edition
HDD: (1) WD Raptor X 150GB (1) 300GB Seagate SATAII & (1) 500GB Seagate SATAII
Optical Drives:2 Plextor 810SA DVD-RW Combo
PSU: Tagan BZ 800W
Case: Antec 900
OS: Vista Ultimate 64bit

Memory set to 1066
Timings set to 5-5-5-15
Dram voltage 2.20v
CPU voltage "auto"
NB "auto
SB "auto

I am running Vista Ultimate 64 bit.

Now for the problem.
I noticed today that my CPU gadget on the desktop was showing ram total of 3326MB and I know I have 4GB installed and it use to show 4094MB.

So I got to checking found that several programs were reporting the same. See photos.
Everest

Windows system information

Task Manager

This is Task Manager a couple of weeks ago.


I have ran memtest86+ for several hours and no errors. I ran Windows Memory Diagnostics Tool and no errors. I took out 2 sticks and they all reported 2046mb. I swapped the memory to different dimms and no changes. If I have 4 sticks installed these programs are only showing 3326mb. I can put which ever 2 sticks in what ever two dimms and it will show 2046mb but as soon as I put 4 sticks in they only show 3326mb.

Has anyone else had this problem, and if so, how did you fix it? Thank you in advance for any help you may give me.

Vista is up to date and just to be sure I ran update again. In post the bios has 4096mb installed. I have a screen shot from August 10th that shows the correct amount of memory. So sometime between the 10th and the 16th of this month something changed the way software programs are seeing available memory. I have tried system restore and no change. Checking updates from last week to see if one of them could have caused it. I have ruled out hardware. I believe it is software based. Still looking!!!!!!!!

What ever it was I fixed it!!! I loaded a ghost image that I had made of my harddrive back in July. Did updates and every program is reporting 4GB again. I believe this problem came about from a tip & tricks page from PC Mag. I may have unchecked something in msconfig / services that I should have left alone. I am going to make another ghost image this weekend and then follow PC Mag's video on speeding up vista to see if it does this again. I would still like to know what happen. Thanks to everyone for their input on this matter.