check all the pins on the mobo, i have put one of these damn things together before to find that one of the pins was not sprung up and therefore not making contact with the CPU, it very easy to miss but defo possiblity. Also have you got a spare PSU floating around yours or a mates house that you could try, its unlikely buit sometimes PSU do not supply the required power to the CPU which can cause this type of issue.
Lets hope its your mobo and the new one solves the issue, good luck let us know how it goes!