Firstly are all the power cables rightly installed? one time id accidently blown the 4pin atx12v cable that goes into the mobo and it was doing something similar... so maybe the cable isnt in correctly or not in at all?
It also sounds like its shorting on something. Is it all secured into the case properly, i know its a pain but u might be better off taking it all out of the case and starting again, dont stick any drives on tho and try starting it when its just a barebones system, ie gfx, ram and cpu. If this doesnt work then you have narrowed it down to gfx, ram, cpu or mobo, if it does work then u know its either one of the other things u have or just bad luck last time