Had same kind of experience with a Asus board years ago.. comp powers up, gets the first boot screen and then suddenly turns off.. tried dofferent psu and stuff but didnt work..
Turned out there were some burned capacitors.. do you see any bad caps?
I've been over the board with a fine tooth comb front & back. I couldnt see any burn marks/blow caps anywhere...
Totally baffeled on this one. I've been through a lot of mobos & seen all kinds of weird & whackey stuff happen. However it looks like this one is going to get the better of me