Is your old CPU still around? Can you put that into the motherboard and see what result you get with it? If its the same result, check to see if any of the pins in the socket got bent. If they did, carefully try and straighten it out. If you break the pin, the motherboard is FUBAR.
If the old CPU produces the same results as the new CPU, try installing everything on cardboard outside of the case and boot up and see what happens. If it boots up fine, you had a short going from the case to the motherboard.