Thank you everyone for your replies.

I decided to do what the last tech support person I spoke to suggested. I backed up the disk, erased everything on it and re-installed the original operating system. Then I re-installed Finale. Then I pulled some important files back onto the hard drive, and all that's working just fine.

It's the recording part that still won't work, even after I re-installed the original Cubase LE program. "No Inputs" is the message I got when I was configuring the inputs and outputs. Weird. I'm not sure what to do about that, and being able to make MP3s of my demos makes up a big part of what I use my MacBook for.

And somehow I'm able to run Pandora again! So...almost there.