Okay, after obtaining the mother of all Torx screwdrivers (18" blade! Longer than the computer is deep!) since I couldn't find a more appropriately-sized one for cheaper, I opened up my SE/30. Tried replacing the hard drive with the one from my IIsi, and it booted halfway before complaining that it didn't have the right system software, so it looks like the hard drive is indeed the problem. Which is okay, since it's only a 40MB drive and I was wanting to put something a little bigger in anyway.

One other question: the sound is very faint or entirely silent, even when I turn the volume up all the way via control panel, even when using headphones. Any idea what the cause of this would be?