I read through the forums and saw similar issues but nothing seemed to match my problem.

XFX 680i LT / 700w PSU / Ultra grid tower combo from tigerdirect.
2gb DDR2 6400
XFX 8600gt XXX edition

As far as I can tell everything is hooked up properly but I do have a remaining cable from the tower labeled "speaker" that I can't seem to find a place for and have read through the entire mobo manual.
I read on a previous post there should be 3 lights on the mobo, amber, blue, and green? I have an amber and blue, no green. What do the lights mean? I didnt see an explanation anywhere in the manual.

When I pushed the power button for the first time it sounded like it would start-up for about 1/2 a second and then nothing. Now after unplugging and resetting as much as I could, when I push the power button - no sound, no boot, no fans, basically like i'm not pushing the button.

I was about to post a thread asking the exact same thing.
XFX just sent me a new 680i LT after my old one was defective. I get the same symptoms as you. I also use an Ultra PSU in the 700W range. By the way, there are no speaker pins for the case speaker.

I have taken apart old computers and put them back together, as well as upgraded numerous pieces of hardware on different machines before. However, this is my first time building from "scratch." If it were a defective power supply would I still be getting blue and amber LED's on the motherboard?