Long story short, I've got my mainboard and assorted hardware laid out on some cardboard for POST diagnostics. I've got my primary SATA drive hooked up. I've turned it on and off a few times, and this most recent time, I've gotten this error message during BIOS startup:
3rd Master Hard Disk: S.M.A.R.T. Status Bad, Backup and Replace
I've had this error message before, but have typically ignored it. I figured it meant that the third drive I have hooked up is about to go south, which if it fails, no big deal, it's only used for miscellaneous storage. But now that I've got just the one drive hooked up...does this mean the actual platter inside the primary drive?
Skip that...it seems as though SMART was detecting problems with my CD burner, of all things, and was screwing up the POST process. Disconnecting the burner data cable seems to resolve the problem. So it's either the burner or the IDE controller has pooped itself.