DFI X38 freezes on reboot post only

Hello all,

Specs:-
Q6600 @ 3.7Ghz @ 1.52v
DFI X38 LT
NB 1.55
VTT 1.35
4x1GB Corsair Dominator @ 1100MHZ 5-5-5-15-2T @ 2.270v

I have been having some random problems recently, in that around 50% of the time when I reboot my PC freezes during the post. Or if I change a setting in the bios and click save and exit, it'll freeze when posting on the restart. Lastly sometimes after clicking save and exit in the bios, the PC will just go to do a reboot (ie no monitor signal etc) then just stays on doing nothing.

However when I click shutdown in Vista and then turn the machine back on again it's fine, I haven't had one issue

It doesn't do this at stock settings, but I have not idea what's causing it, when the pc freezes it hangs on the following 'Post Codes' 20 and 25, but these aren't in any of the post code explanations on the web.

The overclock breezes through hours of prime95/IBT/gaming/FAH etc, which is why I'm stumped. Any help and advice would be ace!

Cheers

Giles