
Ok, it's not the case
because I opened up a case that I knew worked (because I could boot on that machine, heh) and attached that "on" switch to the motherboard in question, and used that case's "on" switch to power up the MB. Same problem.
Since that configuration was working correctly, I went ahead and put the new CPU in that and tried to turn it on. No dice. So I'm wondering if perhaps I damaged that one while trying to install it. I don't know why they warn you not to press down on the CPU while installing the heat sink, and then make the heat sink impossible to hook up without using every goddamn muscle in your body...
"We are all born originals -- why is it so many of us die copies?"
- Edward Young