P5W DH Deluxe and E6400 overclock problems, need HELP

Hi to everybody.
i have this sistem :

Intel Core2Duo E6400
P5W DH Deluxe Mobo
Corsair TWIN2X2048-6400 ; TWIN2X 2048 MB DDR2 / 800 MHz / 5-5-5-12
Leadtek 7900GT
Western Digital 320Gb sata2
and a 500W power Delux power supply - it's kind a noname, don't know for sure.

I've tryed to overclock to 2,6 fallowing the wusy's guid allmost exactly excepting my ddr timings, i leave it to auto. I'll pushed far, to 2,9 and the same result. When i quit from BIOS, simply it's shuts down, and then its powering up, when i am in windows, and i want to restart, it's strangely shutdown and my hdd make some strange noise like "clang". I am afraid to play the tester because i don't want to damage some part because it was expensive for me. I wish if somebody have a sistem like mine or similary, and overclocked it, please to tell me step by step how to do it exactly to make it work, bios settings and everithing. Really apreciate your further posts, thanks!