Just the motherboard (with the CPU in it, and the heatsink and fan on it and plugged in I'm hoping). Also, did you have one stick of ram in there? I don't believe that you can boot a machine with no ram in it, so you'd need at least one stick to really test.
I don't see you mention this anywhere, I could have just missed it, but do you have onboard video on that motherboard?
Did you find out if you have access to a multimeter to test your PSU?
Also, how are you trying to turn on the computer outside of the case?
I know lots of what I'm asking about is basic, but I'm just trying to eliminate things one at a time.