When I Add Ram; 64-bit Vista Freezes And Won't Turn Off.

I hope someone can help me - and THANKS in advance for reading this!

I have a shiny new gaming machine (well, it's 4 month old now, but still very shiny!) It's a custom built PC from CyberPower.com - who's tech help is somewhat less than helpful (hence this post...)

Here's what's under the hood:
500GB SATA II Single hard Drive
Intel Core 2 Duo E6850 3.0Ghz 1333FSB CPUs
Asus P5N-E 650i SLI Motherboard
Corsair XMS2 Xtreme DDR2/800 RAM - 4 Gb (2X2Gb sticks) PLUS another matching 4 Gigs (see the 'problem' below)
2 NVIDIA GeForce 8600GT 512MB Video Cards
64-bit Vista Home Basic with SP1
Thermaltake 750W PSU
Thermaltake MaxOrb Cooling Fan
plus an extra case exhaust fan (temp never goes over 86)

Background:
I play the Sims 2 with ALL EPs and SPs and TONS (80,000+) of custom created downloads. I kept getting Access Violation errors, and my game would crash. I was told I needed even more memory to handle all my downloads... so I bought another 4 Gb from NewEgg earlier this week. I've already heard that the Sims won't use my new mega-memory. I wanted more memory anyway because I also do a lot of work with Photoshop and run my own website: www.CatherinesJewelryDesign.com. So, I really don't want to send it back. It's supposed to work with my system and I want it to work! :huh:

Here's the problem:
After I install the other 4 Gb of RAM, Vista keeps freezing every half hour or so. It doesn't matter what I'm doing - it is completely random. And the only thing I can do is push the power button for 10 seconds to turn it off. When I take the new RAM out, my PC works great again.

Here's what I've done so far, in order:
I know I installed the new sticks right - I followed the package directions to the letter.
I tried changing the paging file size, but after it crashed I set it back to auto for now.
Swaped out the sticks to be sure they work, and aren't duds. They're fine.
I tried running just 2 sticks in the 'B' slots, but that didn't work at all - I think it's not designed to, but I wasn't sure.
I asked for help on MicrosoftTechNet - http://forums.microsoft.com/TechNet/ShowPo...D=17&mode=1
I updated the BIOS yesterday to version 0901 (it was 0801) - and all seems fine; my anxiety level went through the roof during the proceedure, but all is well now. Well, except, Vista still crashes with all 8 Gigs installed.
When rebooting with all 4 sticks in, it finds the memory: 8192 installed, 8191 useable
All the memory sticks are exactly the same EXCEPT the original sticks are 5-5-5-12, and the new ones are 5-5-5-18. I read somewhere that this shouldn't make any difference. All the sticks are Corsair Xtreme with Heat Spreaders: CM2X2048 - 6400C5 (1.90V ver3.1; 800MHz)
Today, I did Vista's built in Memory Diagnostic tool (I found out about it from C-Net) and it checked all 4 sticks - it says there's no problem with any of them.
I also ran the CPU-Z gizmo that I found out about here - it shows each stick of RAMs "stuff" as being exactly the same as far as the 5-5-5-12/18 numbers go. It also said all their voltages were 1.80 (the stick itself says 1.90) I don't know if this means anything or not. I validated, but did not publish the report. So, I can send it to you if you need it?
After that I was up and running with all 4 sticks (8Gigs) - but then it crashed again after 45 minutes...
... which brings me here to ask for your help :huh:

Do you think the new RAM is at fault - or is there some setting I need to change? I really am not technically inclined ...some may even say I was 'challenged' in this area... This is rocket science! At least, it feels like it to me!

Thank you for thinking with me!
Catherine

BleepingComputer.com: When I Add Ram; 64-bit Vista Freezes And Won't Turn Off.