Please any one, I really am in desperate need of help!

I have a problem with gaming.When I play a resource demanding game like crysis my pc freezes.This happens after a period of 3 to 10 minutes.When I play a game like Warcraft 3 Frozen Throne it does'nt do this.I am in desperate need of help.The exact description of the 'freeze' : Screen loses power (goes into power save[exactly like when screen is on but not pc]) then computer sound continues to play but in 2 second loop ( tik-tik-tik-tik) and then it just keeps on doing this until i reset it.(power button doesnt work - need to use reset button )[and in restart windows does not ask if i would like to boot into safe mode)

My NEW system specs:

MSI K9N Neo V2 Motherboard
AMD 64 X2 5400+ CPU
2 Gig 800FSB Ram ( transcend )
NVidia Chaintech 9600 GT 512 mb ddr3 256 bit GPU
Seagate 500 gb Barrucada Sata 2 drive
550 watt Gigabyte superb Power supply
Windows Vista x64 Ultimate edition

I've got the following cooling :

3 ball bearing case fans.
1 Hdd cooler.

And my entire systems temprature never exceeds 45 degrees celcius as a maximum ( usually runs at 35 - 38 degrees under load)

What I have done to try and fix this and have not yet succeeded :

First : Old PC specs :

MSI K8N Neo V3 motherboard
AMD 64 3000+ CPU
1 gig 400 FSB Ram
Nvidia chaintech 9600GT GPU
Western Digital 160 gig IDE HDD
A open 400 watt power supply
Windows XP Proffesional SP3

The following things I have done :

1. Bought all of the New system hardware except for the GPU
2. Exchanged the GPU at suppliers ( checked if GPU has different serial number and ensured they did not give back the old one)
3.Uprgraded to windows Vista.
4.Changed Bios setting of motherboard back and forth between optimal and fail-safe defaults.And mannualy disabled any performance enhancing bios setting)

I have worked with computers for the last 12 years. I have never ever encountered any situation like this.

PLEASE DO ADVISE ANYONE , I REALLY NEED SOME EXPERTISE ON THIS

After installing Windows Vista yesterday I downloaded Nvidia's Drivers.And my motherboard drivers update bi-daily with MSI Live update.

Yes it happend to old system aswell.Purchased the new system component by component checking after every purchace if it had not solved my problem.Have spent more than 700 US dollar thus far.

Will download memtest 86+ and prime95 now and run immediatly start running both tests.

Thank you for replying will post results as soon as done.

Well, seems you've covered everything, except maybe one thing: faulty home circuits?

It's happened only one, and about 10 years ago working for a LAN team, one of our VPN users kept screaming about random reboots/blue screens, so we went through the exact same thing you did; chance every component one by one and formatting.

Didn't fix the problem... I can't remember who thought of trying out a UPS, but that worked. Massive old 1400 UPS fixed it all (only model we had at the time)... he hated the noise it made, but it kept him working heh.

EDIT: vonbose, he already swapped his 9600

I am inclined to suspect a sound driver issue. Turn down audio acceleration, or disable sound entirely to test it.

Ohk i ran prime 95 for 30 mins without any errors.The blended test.

Then next I saw jtt283's post...So I tried it.

After disabling sound in device manager I just played Crysis for 30 mins without any freezes.

I will continue to test this for the whole weekend and keep this post updated.

Thanks everyone for replying so soon after posted.

If the soundcard is the problem what would you suggest ? Inserting pci slot card? Currently was using onboard ( Realtek ALC88 )

And you mentioned turning down audio acceleration.Where would I do that in windows Vista? At present I'm a Vista user for about 4 hours

I was using onboard sound.

It seems as if the sound issue have now solved the problem.Played Crysis 3 hours without any freezes.Also started testing different games.All seems to work perfectly thus far.

Playing without at the moment.Suppliers only open on weekdays so I'm gona have to wait for sound

I had this prob. once,and it was due sync with the sound card and gpu.Is the sound card by creative ?.Did you disable it in the bios,while testing with out sound?

Thinking a bit more about this, it sounds more like a power problem to the vga caed.
The vga card will use more power when it is pushed to the max. If it does not get what it needs, you will get strange results like yours.
The power comes both from the 6 pin pci-e connector, and also from the pci-e slot.
On your mobo, is the vga card inserted into the primary slot which should be getting the full 75w spec power?

If your psu is modular, are the vga leads secure?
Can you try a different plug for the pci-e power lead?

I can find no info on a gigabyte 500w unit.
Is it possible that the psu is defective or marginal? Your old 400w unit might have been giving the same symptoms because it was underpowered.
Can you try a different PSU?