I'm running out of ideas here, about the only thing I can think of to try next is run the cpu up in another pc. I can't seem to find the skt 478 series boards on the Asus website anymore (they've hidden them well this time) but from what little info I found on the net it looks as if your board was pre the "Asus crash free bios" that came with models like mine.
Is there any way you can test it in another pc?
Edit: Found your board on Asus USA website, Asus Australia seems to have archived them, it has crash free bios2. It should have just refused to boot if the oc was too high but you should still be able to get to the bios and reset the bios default settings. The fact that you can't leads me to wonder if in fact it is the board, aside from testing your cpu in another board and a different cpu in your board I really can't think of any other way to find out what the problem is.