Need help with my homebuilt system

OK ladies and gentleman, I have build my computer system, its my first one
I have a major problem with playing games
My computer totaly crashes while in game with black screen and looping sound. sometimes with just still image but rearly
Games that do that:
AirRivals: sli or not
Requiem: SLI or not, but more often with SLI
Dead Space: window mode or not

Games that dont
Call Of Duty 4 (200+ hours) it game me *** couple of times, that all, froze couple of times, thats all
Unreal tournament 3(well didnt play it for more than 3 hours)

i have tired to do:
switching video cards between the 2
Scanning RAM with Memtest (my memory is technicly not on the approved list but correct Mhz)
Using 667 RAM

I am using latest Drivers

SPECS:
OS Name Microsoft Windows XP Professional
Version 5.1.2600 Service Pack 2 Build 2600
System Manufacturer NVIDIA
System Model 132-CK-NF78
System Type X86-based PC
Processor x86 Family 6 Model 23 Stepping 6 GenuineIntel ~3000 Mhz
Processor x86 Family 6 Model 23 Stepping 6 GenuineIntel ~3000 Mhz
BIOS Version/Date Phoenix Technologies, LTD P08, 9/9/2008
SMBIOS Version 2.4
Windows Directory C:\WINDOWS
System Directory C:\WINDOWS\system32
Boot Device \Device\HarddiskVolume1
Locale Russia
Hardware Abstraction Layer Version = "5.1.2600.2180 (xpsp_sp2_rtm.040803-2158)"
User Name SHURIK\Shura
Time Zone Pacific Daylight Time
Total Physical Memory 2,048.00 MB
Available Physical Memory 1.55 GB
Total Virtual Memory 2.00 GB
Available Virtual Memory 1.96 GB
Page File Space 3.85 GB
Page File C:\pagefile.sys


VIDEO : leadtek 9600GT EXTREME SLI factory oc
RAM Mushkin PC2-6400 (part #996603) no oc
CPU core 2 duo e8400 no oc
Mainboard: EVGA 780i Bios P08
Temperature seems good, 40-50 for cpu, 50-60 for motherboard

Please help, i am so tired of trying to resolve the issue. I feel like beating this thing with the baseball bat, just feel bad about spending about 1500$ or so

Also EVENT logger in admin tools never captures the problem so i cant look what is going on

Download nTune from nVidia 's site and lower the clocks on the video cards. See if that fixes it.

Try with a single card too, like MaDMagik said.

That GameXStream 700W is more than enough for 9600GT SLI. We can rule out PSU overload IMO. It's a good brand too.