Windows 7 64-bit conflicts with HD 5970?

Hello all, I was wondering if anybody can help me out with a problem. I have searched and searched and found that this would be a good place to ask for help.

After playing Arma 2 (max settings) for about 5-10mins. I get horizontal lines flickering, and a complete shutdown. I mean the whole thing just turns OFF. After a couple of seconds it tries to reboot except it either shuts off again, or it reboots with no input to the monitor. Which points directly to the video card doing something strange

It's a brand new build, so I haven't had a chance to test it with other games.

My build:
Intel i7-950 Core 3.06Ghz
Intel DX58SO Extreme Series Mobo
6GB OCZ Tri-Channel DDR3 Memory
80GB Intel X25 Internal SSD
1TB 7200 Barracuda HDD
Kingwin LZ850 850watt
Creative Blaster X-Fi Titanium PCIe
PowerColor HD 5970 PCIe x16

Reviewers said this card would work efficiently with a 650w PSU

The case is medium sized, but it has 3 fans connected to the PSU so they're running full speed all the time. Even with the case open the same thing happens.

Why are some hardware reasons that would shut off computer as it it were a power outtage?

I appreciate the help

Never mind I fixed it.

It turned out to be a bad stick of ram

I took the Memory Sticks out and tested them one by one...

2 of them, I was able to play for hours...one of them allowed me to play for 5 minutes.

Problem solved.

I hope this will benefit others because this drove me crazy for 2 days.

The funny thing about it is that I bought OCZ High performance tri-channel gold memory..in hopes that I wouldn't have to worry about this...

They boasted that they test their memory in tri sets to assure there are no differences

HA! marketing...have a good day