System freezes after few hours

Hello, I've successfully install snow leopard 10.6.2 on my system:
Gygabyte GA-P55M-UD2 bios F8
Intel i750 + 4Gb DDR3 1333 7-7-7 OCZ
Nvidia 8800GTS 512Mb
Udate 10.6.3

but my pc after 3-4 (sometimes 5-6) hours that is on always freezes no matter what it do (listen music with itunes, download with amule or nothing)

If I boot my system from iBoot CD the PC is rock solid and don't freezes, but if I boot from hard disk freezes, so I think that depends from the efi files.
I've tried several options from multibeast (rekursor, asere e pcefi 10.6 as boot, all type of graphics injection via apple.boot, dsdt or nvenabler, several option of dsdt with or without speedstep) but no luck.
I've tried also the EFI file from tonymac but always freezes.
I've also used onyx for repair permission and kext utility to rebuild extensions.mkext
So the question is what EFI and kext used the iboot cd?
What else can i try?
It may depends from kernel (I see that cd iboot uses 10.0.0 patched kernel)?

Thanks for reply!

sounds a bit like a memory problem. Perhaps set looser timings, 0r let memtest run for a night.

Also people might be able to help you beter if you provide us with the kexts you are using

Hello, I've set memory at 1066 with standard timing and I've use the new multibeast gigabeast option installer but still no luck the system freezes randomly.

With the iboot cd all is ok...