Sounds like either the processor is kaputt or something is shorting the motherboard. What I always do in a situation like this is completely remove the motherbord from the case, put it on some sort of non-conducting material (like the bag most motherboards come in) and then build the 'computer' separate from the case.

If it works then, you'll know something about the case was shorting out the motherboard. It could be one of the pegs the motherboards rests on, in which case you could use some of those small plastic grommets to put between the pegs and the motherboard.