Hi,
i write you for a problem that i've met with Asus P5B motherboard.
First, i apologies for my english level and my grammar error.
This is the problem: i have a Asus P5B motherboard with a Intel Core 2 Duo E6600 CPU and a Enermax Liberty 620W as PSU.
I tried to overclock this system, bringing FSB to 333MHz and CPu to 2997 by BIOS. I set the Ram (2x1GB Corsair PC6400) at
666MHz. I saved the settings, then reboot the PC (i make all this procedure by bios, not from the software Asus in the OS)
but PC stops totally. I tried to reset CMOS (setting jumper as the motherboard guide say and taking out the battery), turn off PSU then turn on,
but the problem persist. The PC didn't boot at all. When i press the button, led enlight for some istant, the fans also
move for some istant but everything stop and and turn off.
I hope that i've correctly explain the problem and didn't made too many grammar error.
If you can't understand what i said (or what i mean), please tell me, i will try to explain me better.
Thanks for every help that you could give me.

I'm guessing that you've set the RAM speed incorrectly, I'm not sure though. It sometimes gets confusing because of theoretical DDR/QDR speeds vs actual frequency settings.

The CPU:DRAM ratio should be 1:1, so even though you have PC6400 RAM, it should be underclocked to match the CPU. With the CPU running at it's default bus speed of 266MHz (1066MHz FSB), the RAM should also run at 266MHz (DDR533).

With the CPU bus overclocked to 333MHz (1333MHz FSB), the RAM should be set to run at 333MHz (DDR667).

With 266 FSB ram works at 800MHz (i think that the DPU:DRAM ratio is 3:2), the motherboard sets this speed automatically. If i set this ratio with 333MHz FSB, ram frequency was be 1000Mhz, so i set e lower speed, as you said i set ram frequency at 667 (not 666 as i said before, forgive me) Surely i wrong in setting something, but i think that the bios parameter (including RAM speed) was resetting with the reset of cmos.
Thank you for your help and your kindness.