Win7 64 freezes solid

Hi!
I need some help, searched many forums, but found solution nowhere.

Bought new motherboard, processor, RAM, system HDD. Installed fresh (legal) Win7 (6.1) 64 bit Ultimate Edition (Build 7600).
Installed drivers, programs. So my PC is relatively fresh.

Yet sometimes, Windows 7 freezes. And by freeze, I mean freeze solid. No ctrl-alt-del, no power button, not even response from Caps/Num/Scroll lock (led on keyboard). Only reset helps.
Random freezes happen: Mostly when using Opera browser (usually after I open a new tab, or close one), but it just happened while playing Settlers II 10th anniversary (after zooming in).

The problem is that I can't really reproduce the error. It happens 1-2 times a day if I use my comp for like 6 hours or so. Sometimes, it doesn't freeze for 3-4 days.

Additional mystery: before reinstall, I had WinXP with another MB, proc, RAM, sys HDD. It randomly rebooted (like pressing reset randomly). MB was a replacement used ASUS P5KPL-CM I got from my dealer till they tried to get ASUS to repair my origilan MB. (Nevermind...)
So, I took out MB, processor, RAM, and installed it into a different computer. No random reboots in that one so far. I bought my new MB-proc-RAM combo, installed in my comp - no reboots, but random freezes with Win7. 0.o
I bought a new Samsung 160 GB HDD, and (clean) installed system on that one. Same shit.

I don't know if there can be a connection between the two things...

It is not the VideoCard, my old comp used to reboot without the VC, using the onboard one. I have the latest driver.
The AC adapter is relatively new. (<6 months.)
I have a backup HDD that is unchanged, and my age-old ATX house.

System is not overclocked in any way (I use ASUS EPU, but that is just a power management utility, and TurboV EVO is running, but it doesn't do anything to the system).
Running GTA4 with high graphics, high AI - no problem at all.
Running VMWare with 2 virtual PCs (1 32bit win7, 1 32bit XP) - not even a spike, perfectly smooth.
So freezes have nothing to do with system performance, overusing resources or whatever.

Any ideas where to start investigating? (Eee, the big problem is that for every idea, I have to test for about 1 week to be sure that it solved the problem :/. Freezes are random and rare.)

Thank you!

System specs:

proc: AMD Phenom II X6 1055T

MB: ASUS M4A89GTD PRO

RAM: 8 GB DDR3 (Kingston)

HDD:
System: 160 GB Samsung HD161GJ
Storage: 500 GB WDC WD5000AAKS-00D2B0

Graphics: Gainward 9600 GT (Nvidia, 512 MB)

Monitors:
1st: LG Flatron L1915S
2nd: LG Flatron L1918S

Windows Version: Microsoft Windows 7 (6.1) Ultimate Edition (Build 7600)
DirectX Version: 11.0
Avira Antivir personal

Thank you for your help!

Yep, read through most Win7 freeze posts, but found nothing useful...
The thing is, I didn't find any other thread where the freeze was as complete as in my case (no mouse, no Caps lock, totally frozen).

Is there a built in event logger? Maybe some process gets called before the freeze or something that I could find this way?

The event logger is under control panel administrative tools event viewer. Translate to your language if you don't have english OS. Since mouse, and no Caps lock my guess is a complete CPU stop. Try boot with superboot CD and do some tests. http://www.ultimatebootcd.com/

I know you've tested the RAM in another machine, but have you run memtest86+ on this machine?

It'd also be interesting to know where the temperatures are in this thing. Memory probs and processor overheating (triggers core shutdown to protect it) could lock it down to where you have to cold-boot.

Thx for the replies! I have found a clue.
If I remove the video card, and use the onboard one, no freezes happen. Put back the video card, freezes do happen.
Freezes don't happen on random. Some combination of web pages are open in Opera, and I close one page (or Opera itself) while one with many pictures (eg. picasa) is still loading - it freezes.
It is not only Opera though, finished video playback (SMPlayer with HW acceleration on, duble buffer on, in direct3d mode) - only happened once, or a game (not resource-demanding at all) also froze it.

The common thing is that something has to happen from software-side to make it freeze, system always freezes after a click or a zoom-in, or video window auto closing.

System also freezes if I remove the (idiotic) switch-card from pci-e slot1 to make pci-e slot 2 under my video card fall back from 16x to 8x.

Tests I have run:
Asus PC probe shows no overheating or voltage problems at freezes (I have it always on in the 2nd screen). Ram never above 22%, CPU never above 10% when freeze happen.

Stress test doesn't make it freeze (Asus PC Diagnostic) - Graphics, CPU, RAM stress - no problem.

GTA4 with high graphics, high AI - no freeze.

Original windows7 drivers, original bios - freezes happen.
All new drivers (yes, video driver after fully sweeping old drivers), newest BIOS - freezes happen.
No driver for onboard video card - freezes happen.
Dreivers for both integrated and dedicated video card - freezes happen.
Reinstall Windows 7 with only a few programs - freezes happen.

My video card (Gainward GeForce 9600 GT) seems to be ok, had no problems with it, and it works fine when used hard.

No viruses, adwares.
No strange noises.
RAM is ok (Windows RAM test), HDDs are ok (Windows HDD test). (I won't run Memtest, since video card seems to be the problem.)
Event logger hold absolutely nothing from times before the freeze, no events or errors logged.

So, any suggestions now?

Can it be the mother board? We all know that if I take it to the shop, they'll run a few tests and say everything is perfect. (Especially ASUS, they do everything to ditch warranty issues).

Check the BIOS, it is usually an option for disable the onboard GPU (Graphic Card). Think it reads "onboard devices" or something, you can disable onboard soundcard, network card. Depended on what BIOS you have, you can press a key during the BIOS startup, often the key is "DEL". Then you get in the BIOS. Change with care...

Thank you, but it can not be done.
Onboard video can't be turned off in this BIOS, but the priority is set right (PCI-GFX0-GGP-1GFX). Other minor settings don't do any right for me, so I didn't fiddle with them.

Any other ideas? I'm kinda out of ideas myself...

Guess it'll be take back to the shop...

Isn't your card a PCI-Express card?

Yes, it is pci-e. Works at speed 16x. (PCI in bios settings refers to the pci-e slot, it is just abbrevated PCI.)

Hmm, I'll install another browser, and try to narrow down the problem even more.