This is not the first post of this problem with Asrock p67 boards:
Various things to try have been suggested.
However I will give u my own experiences
I purchased a b2 p67 extreme 6 in february,it worked fine.
Yday my replacement b3 board arrived:
On initial boot up it gave the d6 dr.debug code .(keeping f2 pressed it gave a 0d code).
To cure the problem ,I tried:
1.Disconnecting the second cpu fan and 2 pci slot exhaust fans(running on 5v) in order to give the maximum power at startup to the gx card.That didnt work.
I considered trying a different gx card (see sig),but since my system had been working before,there was no reason it shouldnt work now.
What "fixed it " for me was
(a)I removed and reseated my 460gtx(in the first pcie slot),and made sure the pcie locking tab clicked home.
The last time ,I just moved the locking clip so that it engaged with the gx card tag as locking it fully is a pia when you want to remove the gx card .
(b)Rechecked my 2x6 pin power connectors to the gx card and left all extra fans etc disconnected.
This time the pc posted/booted ok.
Since then I have reloaded my 4.8ghz overclock,my gx card overclock and reconnected the extra fans and my icy dock(http://www.overclockersclub.com/reviews/cremaxicydock/ ,I use the temp probes on the memory modules).