Sorry to dig up and old thread, but here are the latest developments:
I took the board + PSU out of the case, and systematically tested everything by disconnecting it and seeing if the problem would go away. I deemed the problem to be the PSU.
I took the PSU out of my roomate's computer and it booted the computer normally. So I was pretty sure my PSU was the problem and I went through the RMA process and got a new Seasonic.
I just got my new one, hooked it up, and same problem... I tried adding a 2nd hard drive, but as hinted at in http://www.silentpcreview.com/article28-page5.html
but to no avail. Could the PSU just not work well with this board?
The only other PSU's I have spare are 20 pin instead of 24? I plugged one in temporarily and the computer seemed to work, but is it a good way to run it like this? Any advice on buying a new PSU (silent) that might work? Or just use my spare?