Picked up a new motherboard to replace one that had given up the ghost. Snagged an ASRock Z68 Extreme3 Gen3.
I dropped it in and it fired up fine using the onboard DVI. I dropped in my GTX 460 and it hangs at B2 which appears to be "Legacy Option ROM Initialization." I dropped an old GT9800 in and it fired up first time.
So after doing some digging and not really coming up with much I'm left with three possibilities that I can think of. Bad video card, bad power supply, or something hinky in my BIOS.
The PSU has 2 12v lines running out of it and is modular. I've checked both lines and both sockets in the PSU by trying the 9800 with all the combinations and all the cables and sockets appear to work fine. The hardware monitor in the BIOS also shows the 12v rail at 12.3-12.4v.
I haven't been able to test the GTX 460 in a known good machine yet as I don't have anything with a PSU in it that can push that card.
If anyone has any clarification as to the meaning of the error Dr. Debug error message B2 "Legacy Option ROM Initialization" and why it might be occurring only when I drop in my GTX 460 I'd love to hear it.
From the name of it, it sounds like it's trying to read/display to BIOS info from the GPU and can't for whatever reason. I just did a quick Google search on it, but it doesn't look like the people that have reported the issue have ever found a fix for it, unfortunately. My guess is that it's a mobo BIOS issue, but I don't know anything about the BIOS of that ASRock mobo, so I don't really know where to tell you to go from here. Maybe there's an option to turn off Legacy ROM support (not needed for a newer add-on card anyway)?
The only thing I saw that fixed it was a new mobo, but I don't see how that's the problem here, when it works with the 9800 GT. It COULD just be that the mobo doesn't play well with the GTX 460, I guess, but you'll need to see if there's a BIOS update to fix it.