Strange OC problem

[Phyl690]

Hi,

My system :
C2D e6600
Sapphire x1950xt 256m
Asus P5W DH Deluxe (bios 1707)
4x1gb of OCZ Platinum R2 DDR2-800
OCZ GameXStream 700w
Windows Vista Ultimate x64

For now over 6 months, the system was overclocked @ 3.6ghz with the following setting :
CPU : 1.4375v
RAM : 2.0V (only 2gb of ram)
FSB : 1.4v
MCH : 1.75v

it was perfectly stable.

Now last night, i bought another 2gb of ram and the system freeze at 3.6
it failed orthos in 3s and mem test in 5s

I boost voltage on ram at 2.1, FSB at 1.5 and MCH at 1.85v.
now it freeze in memtest in over 1min.

I test the ram all night at stock (2.4ghz, ddr2-533), rock stable with over 9hours of test.

same for 3.00ghz, ddr2-667 (with 1hour of testing without problem/error/freezing)

Now, why its freezing at 3.6 ?
Im running memtest @3.514 (390FSB), and it seems ok for now.

Thank for your help,

 

[Phyl690]

Update : it failed memtest (test 5) at 390mhz FSB
trying at 385 now.