The 1.2b3 bios for me would only post with older cpu's. It wouldnt post with my E8600, Q9450 and Q9650. Well it would post but would lock up as soon as it did. I couldnt even get in to bio before it locked. This may be your problem though it is strange that it would boot into windows that first time. I had to throw a Q6600 in to get it to post far enough to install the 1.2 bios. Even though are problems are different, it could be bios incompatibility with the 9450. Hopefully you have access to an older chip to try. I'd say E8500 or older or any 65nm quad. Good luck!