Ok, here's what I have:
Intel Quad Core Q9400 2.6GHZ
Gigabyte mobo GA-P43T-ES3G
G. Skill F3-10666 ram 4 ram sticks X 4 = 16 gb
Zalman CPNS9500 AT2 CPU cooler
ATI Radeon HD 5770 video card
600 W PSU
I have gotten my CPU overclocked stable at 3.4 GHZ with:
CPU Multiplier 8.5 (.5 from fine tuning) 1.275 Vcore in Bios (1.232 in CPU-Z)
FSB 400 MHZ,PCI 100 MHZ, MCH 400, 3:5 FSB/DRAM, SPD 3.33D, stock timing 9-9-9-25 108 2T, Prime95 runs 64 degrees after 10 minutes...
anything above this and it's unstable no matter what I try. I've upped the Vcore to 1.320v, NB to 1.4 and DRAM to 1.6 with no luck. it won't even post.
I have been able to get FSB 415 MHZ to work if I turn down the DRAM speed to 333 wiht 3.2B SPD. Any ideas on how I can keep this cpu clock speed and get my ram up to 666? No matter what the CPU is, if the Ram is set above 1333then it won't post.
When you set your ram above 1333 and it won't post...well, this could be because your ram doesn't like overclocking, or the memory controller in the north bridge can't handle that...
And that could be because, unfortunately that's not the best lga 775 board to overclock with...and from 2.6 to 3.4 is already 8000Mhz so you may have hit your wall...
I would recommend to keep trying though as it is trial and error most of the time till you get ideal settings...and try finding a specific detailed guide for that cpu...it could tell you something you don't know or something we might not tell you here...
Here's one more thing you can try; try raising the pcie frequency a bit...It actually might help you get stable...just don';t raise it too high cause it can corrupt your data if you go really high...
and try doing exactly what jitpublisher suggested... well good luck
Here's how you can find out if it's the CPU settings or the memory settings:
Go into the BIOS settings and lower the System Memory Mult as low as you can. Then try increasing the CPU up to a max of 1.45 volts or until load temps reach 70 C. If you can go substantially higher than 3.4 GHz ounder load, your memory is holding you back.
At any rate, considering that you have a Q9400, I suspect that you just about have your system pushed as far as it can go.
Yeah I know I heard of the stories as well but if you raise it slightly it normally does nothing...in any case if your system is stable without raising the PCI clock then you don't need to raise it and you're perfectly fine...