Random Lock ups

Question

I'm using K9N2-SLI plat with Bios 3.5, AMD64 X2 6400+ Black Ed., 4GB ram (2x2GB Cas 4-4-4-12 T2 matched set), XFX 8800GTS(92) 512, Corsair TX650, Artic Cooler Freezer64 CPU H/S running Vista64 Home Premium Sp2. I'm having random lock-ups during 3D games. Sometimes it locks up after 30 mins in game or sometimes it locks up after days of playing, I can't get it to reproduce the lock up at will. I have read alot of post about this motherboard and it seems it comes down to power supply. I had a New Apevia Beast 2 rail system but after reading the posts I returned it for new Corsair TX650. At full load CPU cores never go above 47c and Idles around 30-31. Ran mem test over night with no errors. Did notice in Mem Test it stated Ram was set at Cas 4-5-5-18 T2. I went to BIOS and set the mem for Volt 2.0 Cas 4-4-4-12 T2. This did reduce the lock-ups to the point I thought I had it fixed. Than today I locked up twice. When it locks up computer becomes unresponsive last sound repeats for few seconds and the only way to resume is to press restart button. I have tried with Cool n'quite on and off, DOT is never been on. Computer runs fine in 2d operations. It's only when I go into 3d games. Video Card has been tested in other machine and is working fine. My game sometime requires me to stay logged in over night to Sell goods. Every morning this last week computer has froze sometime during the night. Crysis plays fine for hours, It seems it happens in not so demanding games, Aion, Knight Online and Wow. All power plugs are plugged, fresh install of Vista, Newest drivers from web site, Bios update via the Forum USB key app. Would really like a reliable computer. What am I missing? Let me know if you need any other info.

Answer 1

OK I ran single stick and it locked up quicker. I went to BIOS used optimized defaults with only changing the volts to 2.0. and it locked up again. It's lockups seem longer if I change mem setting to 4-4-4-12 T2. I used CPU Z and noticed few things.
The memory report from CPU-Z:
DIMM #            1
   SMBus address      0x50
   Memory type      DDR2
   Module format      Regular UDIMM
   Manufacturer (ID)   A-Data Technology (7F7F7F7FCB000000)
   Size         2048 MBytes
   Max bandwidth      PC2-6400 (400 MHz)
   Part number      EXTREME DDR2 800+
   Number of banks      2
   Data width      64 bits
   Correction      None
   Nominal Voltage      1.80 Volts
   EPP         yes (2 profiles)
   XMP         no
JEDEC timings table      CL-tRCD-tRP-tRAS-tRC @ frequency
   JEDEC #1      3.0-3-3-9-12 @ 200 MHz
   JEDEC #2      4.0-4-4-12-16 @ 266 MHz
   JEDEC #3      5.0-5-5-18-23 @ 400 MHz
EPP timings table      CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
   EPP profile #1 (full)   4.0-4-4-12-22-2T @ 400 MHz (2.000 Volts)
   EPP profile #2 (full)   4.0-4-4-11-20-2T @ 400 MHz (2.000 Volts)
since I was using EPP profile 1 I noticed that motherboard is running my memory at 4-4-4-12-24(EPP profile shows should be 22)-2T. Should I change to match memory? or should I try JEDEC #3 @ 400MHZ
Next thing I noticed was The chipset is stated as 740a not the 750a
Chipset
Northbridge      NVIDIA nForce 740a SLI rev. A2
Southbridge      NVIDIA nForce 740a SLI MCP rev. A2
Graphic Interface      PCI-Express
PCI-E Link Width      x16
PCI-E Max Link Width   x16
Memory Type      DDR2
Memory Size      4096 MBytes
Channels         Dual
Memory Frequency              400.0 MHz (CPU/7)
CAS# latency (CL)              4.0
RAS# to CAS# delay (tRCD)   4
RAS# Precharge (tRP)           4
Cycle Time (tRAS)               12
Bank Cycle Time (tRC)          24
Command Rate (CR)             2T
I've tried loser setting 5-5-5-18 and still locks up.