if you had this same problem on the previous rig with the same psu, and you;ve installed anew mobo and cpu with heatsink and fan and the fan aint working on this one then i think a faulty psu is a strong possiblity. i dont know exactly how a psu works, voltages on the rails etc, but i winder is it possible that it isnt supply sufficient power to the motherboard?? have u a independant pc store near you that could test your pc, they'd probably charge a minimal fee for this
ahh ignore, i see sayso has offered to help