[Help] PC Freezes randomly during Games/Streaming vids!

[xAjayy]

Hello,

So my problem is currently what i have around 2weeks orso,
Is that when i play games (Example:Bf3) randomly different timings my,
PC Freezes, Screen still on.. cant move mouse or anything else, And also
If the freezing happens i hear the last sound what iv heard (example:gunshot)
Looping, just repeating itself! The onlyway to fix the problem is manually holding the powerbutton and turn it off/on!.
The most commen when i get the problem fast, if i enable the SLI in Nvidia
How i reduce the problem currently is by: Turning off 2 Cpus in BIOS, also disableing SLI

I got:

Desktop DELL XPS 730.

(Intel Core Extreme 2 QX6850 3.00GHz)
(4cores)
(Got 2 NVIDIA GeForce GTX 280)
(1000W Powersupply *dont know name but if neccesary tell me!)
(Windows 7 Ultimate x64)
(6GB Memory)

Here you got some more info!*Screenshots*
EDIT: The screenshots are taken with only 2CPUS Enabled!/SLI Disabled

Those are the normal temps when i dont do anything else theng Gaming/Streaming vids.

Also been wondering if 1.5V is good enouf ? Dont i need to change it to 1.65V?

Hope you guys can help me.
Best regards,Ajayy (Im sorry if i posted on wrong place!)