Re: weird startup problem
Start swapping out components, starting with the motherboard.
Course I assume you don't have any testing parts, else you probably would have done this already.
That being said, go out and buy some cheap test parts, or try a friends motherboard, assuming they will let you.
If you don't do that, RMA the motherboard, If you can't RMA the motherboard, buy a cheap one and swap it out.
Its a cycle, if you can't do one, you must do the other.