F2-8500CL5D-4GBPK on GB EP45-DS4 - Boot Problem

[yiph]

Hi,

I just got a pair (4GB) of F2-8500CL5D RAM and I'm using it on the following system:

Motherboard: Gigabyte EP45-DS4
CPU: Q9550
RAM: F2-8500CL5D-4GBPK
Vid card: 9800GT
HDDs: 2x500GB

I put both modules in slots 1 & 3 (BANK_0) for dual channel operation. It failed to boot, did not pass memory test and keeps rebooting. It stops at POST, can't get into BIOS, not even after a BIOS clear.

I put only one module for single channel, it worked.

I put it in slots 2 & 4 (BANK_1) and it works, but not exactly stable POST boot. I was able to install OS (Vista x64) and all software without problem. But sometimes I boot up from cold state (next morning), it goes into memory test and reboots. But after the reboot process, it worked again and boots up into the OS. I never had any trouble with blues-creen crashes or anything if I could get into OS. After 7 hours of prime95 torture test, ran fine. I also ran memtest86 during boot, and it passed the test as well (I only ran it for about 40mins).

My BIOS settings as follows:
RAM mode: [Standard]
VDRAM = 2.1V
RAM freq (multiplier): 1066Mhz (3.20B I think)
Timings: 5-5-5-15
CMD rate: 2T


What is the exact problem? Motherboard NB / RAM slot(s) faulty or RAM?

Regards,