No idea.. no one has Q6600 G0 yet heh

weird indeed... i know wrong frequency can cause hdds to disappear but bios settings not to set is a first i heard of this

what do you have SATA set as RAID or AHCI ? first post by BenchZowner had some tips for raid on P5K3 Deluxe Asus P5K3 Deluxe ( P35 Chipset & DDR-3 ) might help

Spoke too soon I'm afraid. It's not the PCI-E freq at all. I switched the system on again this morning and it was back at 2.13GHz. I checked the BIOS and yup FSB is definitely set to 375. BUT! I now know how to fix the problem. If I switch the PSU off for about a minute (at the switch near the power plug) then switch it back on and power on the unit, the settings take effect and wwork perfectly. It's sounding more and more like the CMOS battery isn't it??? Might just grab a new battery anyway. What do you think eva?

SATA is set as RAID so its not trying to run AHCI or anything. Still dont know. I'll take a look through the other thread, thanks eva

try different SATA ports too

JumperFree Configuration Settings
AI Overclocking: Manual
CPU Ratio Control: Manual
- Ratio CMOS Setting: 8
FSB Frequency: 440
PCI-E Frequency: 100
DRAM Frequency: DDR2 1100
DRAM Command Rate: 2T
DRAM Timing Control: Manual
CAS# Latency: 5
RAS# to CAS# Delay: 5
RAS# Precharge: 4
RAS# Activate to Precharge: 9
TWR: 2
TRFC: 25
TWTR: 2
TRRD: 2
TRTP: 8
DRAM Static Read Control: AUTO

Transaction Booster: AUTO
Clock Over-Charging Mode: AUTO

CPU Spread Spectrum: Disabled
PCIE Spread Spectrum: Disabled

CPU Voltage: 1.4125v
CPU Voltage Reference: AUTO
CPU Voltage Damper: Enabled
CPU PLL Voltage: 1.50
DRAM Voltage: 2.10
FSB Termination Voltage: 1.30
North Bridge Voltage: 1.40
North Bridge Voltage Reference: AUTO
South Bridge Voltage: 1.05

Advance CPU Settings
CPU Ratio Control: Manual
- Ratio CMOS Setting: 9
C1E Suppport: Enabled
Max CPUID Value Limit: Disabaled
Vanderpool Technology: Disabaled
CPU TM Function: Enabled
Execute Disable Bit: Enabled
PECI: Disabled

USB Configuration
USB Functions: Enabled
Legacy USB Support: Disabled