simple CPU OC in BIOS crashes

[dameista]

Hi, I have small issue with my OC.
My system:
Gigabyte X38-DQ6
Intel Core 2 Duo E6750 (default @ 2.66GHz)
2x 2GB OCZ Platinum Edition 800MhZ
Antec P185 with plenty of fans and ideal airflow (al cables hidden...)

After some research I found that I should be easily able to set my CPU clock to 400x8 (-> 3.52GHz) instead of the default 333x8 without needing to tinker with any voltages, RAM timings etc...
So I set that option in my BIOS and never have any stability or temperature issues.
Now once in a while my pc just boots with the OC setting disabled. The 400x8 setting is still visible in the BIOS, just not enabled...
Every time I try to switch the OC back on the pc boots as if I set it to an impossible setting. At POST, instead of reading the CPU details, 'counting' the RAM and moving on to the HDD's it just shows the default CPU speed and then 'MEMORY TE' (instead of 'MEMORY TESTING' and the amount of RAM) and then reboots and szitches back to default.
Even setting the OC to 334x8 does not work.
Now after a couple of days I'm able again to set the OC to 400x8 or even 440x8 and my system still remains stable until one (re)boot when the setting is gone again.
It sometimes happens after days, sometimes months,... and I can't really find the cause. It's not like it happens every time I stress my system, it seems completely arbitrary...

Anyone have any ideas what causes this?

Thank already for the help!

 

[redduc900]

Fill out this BIOS template for the X38-DQ6 w/ all of your current settings at 333MHz x 8, and post pics w/ CPU-Z open to both the SPD and Memory tabs. And I assume you already have the latest official BIOS revision F8, or Beta v. F9J?

[B]MB Intelligent Tweaker (MIT)[/B] 
Robust Graphics Booster: 
CPU Clock Ratio: 
CPU Host Clock Control: 
CPU Host Frequency(Mhz) : 
PCI Express Frequency (Mhz) : 
C.I.A.2: 
Performance Enhance : 
System Memory Multiplier (SPD) 
Memory Frequency(Mhz): 
DRAM Timing Selectable : 
[B]Standard Timing Control[/B] 
CAS Latency Time: : 
DRAM RAS# to CAS# : 
DRAM RAS# Precharge : 
Precharge Delay(tRAS) : 
[B]Advanced Timing Control[/B] 
ACT to ACT Delay(tRRD) : 
Rank Write to READ Delay : 
Write To Precharge Delay : 
Refresh to ACT Delay :  
Read To Precharge Delay :  
tRD : 
tRD Phase Adjustment : 
Command to #CS Timing: : 
[B]Clock Driving and Skew Control[/B] 
CPU/PCIEX Clock Driving Control : 
CPU Clock Skew Control : Normal 
(G)MCH Clock Skew Control : Normal 
[B]System Voltage Control[/B] 
DDR2 OverVoltage Control : 
PCI-E OverVoltage Control : 
FSB OverVoltage Control : 
(G)MCH OverVoltage Control : 
MCH Reference Voltage Control : Normal 
DDR Reference Voltage Control : Normal 
DDR Termination Voltage Control : Normal 
CPU GTLREF1 Voltage* : 
CPU GTLREF2 Voltage* : 
CPU Voltage Control : 
Normal CPU Vcore : 

[B]Advanced Bios Features[/B] 
CPU Multi-Threading 
Limit CPUID Max to 3 
No-Execute Memory Protect 
CPU Enhanced Halt(CIE) 
CPU Thermal Monitor 2 
CPU EIST Function 
Virtuaalization Technology

 

[jason4207]

Did you do any stability testing? What is your definition of 'stable'?

My money is on your RAM not being set properly after your changes. When you OC the FSB you are also OCing the RAM, and you most likely need to change the RAM divider to bring your RAM back down to a speed it can handle.

 

[dameista]

Thanks already for your replies

@redduc
I'll be needing some time to get you all those details
I haven't been looking at a BIOS update or anything because most of the time my system just accepts the 400x8 or even 440x8 setting for months at a time without even a glitch. To be sure, I'll look into the BIOS update.

@Jason
My noob-definition of 'stable' is when my pc doesn't crash
As I have said, my system actually always runs fine. Even with this problem of resetting the OC settings itself my pc does not crash. The issue just comes after a manual reboot... So I'm pretty sure it has nothing to do with the OC setting being too high. Also whenever I have this problem I can't even get a 334x8 setting to work...

Your suggestion of the RAM settings being incorrect, would my pc be able to run 440x8 perfectly fine for months and only then just reset the OC setting? (again, without crashing, so it does it under completely stress free circumstances)

The whole point of what I'm aiming for is not having to adjust anything apart from the FSB. And for 80percent of the time that works nicely... just sometimes my system does not accept an OC setting which has been proven to work before and will surely work again in a couple of days...
BTW a friend of mine has the same CPU and mobo and 'lesser quality' RAM and does the exact same OC as me and he never has issues.

Thanks again for your help!

 

[jason4207]

The RAM might be set with a high divider n which case it is being OC'd way more than it needs to for your given FSB speed.

We'll know what you're working with once you have time to fill in the form and post the screenshots.