New build randomly locks/or shuts down

Ok, firstly, this is my first post here, please direct me to the right place if im posting in the wrong section.

So i got all these components together and its crapping out on me.
Here's what i got...

MSI nf750-g55 Mobo updated AMI BIOS ver. 1.2

AMD Phenom II X2 Black Edition 550 Callisto (on stock cooling)

4GB OCZ Obsidian DDR3 RAM (dual channel, 2 sticks) Rated at 9-9-9-24 1600

Dual BFG GTS250's in SLI

Western Digital Caviar Black 750GB Sata drive

SilverStone 650W PSU

Windows 7 Ultimate 64bit edition


So i built the machine (using just ONE video card at first), it posted fine with default settings. I installed OS, and it booted just fine.
I installed drivers and such, no problems.
After a couple reboots, the system froze. No BSOD, no messages, just freeze.
Installed second video card.
Freezes continued to happen at random.
Tried updating the bios, went through without a hitch. System still randomly freezes.
Tried to adjust the RAM timings to get them to manufacturer recommended settings (see listed above) Could not get system to boot most of the time with those settings. It would occasionally though. (Mobo wont let me set voltage to 1.65 closest i could get was 1.64 then the settings jump to 1.67)
Removed one Ram stick, ran MemTest on each one. no errors on defaults, but could not get through test with any adjustments (ie manufacturers settings)
Tried running stress tests and benchmarks.
Video benchmarks only work with one video card installed, when in SLI, computer shuts off. no errors, no messages, just immediate power down.
System will still hang either way.

System also shuts down during gaming.

Whats up with it? any ideas? any troubleshooting i havent tried?


Thanks for any help!!

EDIT: i forgot to mention that throughout all the troubleshooting, my CPU will sometimes post as a quad core, even though i never did anything to unlock other cores. This also seems to happen at random.

 

I would check temps

 

I've already installed cpuid and speedfan and all seems to be normal on both. Temps are not anywhere near high when problems occur. (with one small anomaly, speedfan has ONE sensor showing extremely high temps all the time, but ive come to the conclusion based on a lot of testing that it is a non functioning sensor)

Any other ideas?

 

I picked up a new power supply and it seemed to solve MOST of my problems.
SLI works. Havent shut down or frozen up yet.

Now, i just cant seem to get the RAM to run at Rated speeds.
I got the OCZ ram rated at 1600 (9-9-9-24) so i wouldnt have to go through the trouble of OC'ing. Now it seems i have to anyway...any suggestions?