This is getting more and more weird. I left the computer on all night, doing its validation thing, but I don't remember if it said it was validating df0: or df1: (the information disappears from the screen fairly quickly).
This morning, with a blank DOS screen showing, I shut the computer down. When I powered up, the computer booted normally from the hard drive. Just out of curiosity, I inserted a disk into df0: and, working in a CLI window, typed "cd df0:". The response was "Can't find df0:". Just to check, I inserted the same disk into df1:, repeated the command, and the drive read the disk.
So, now I seem to have df1: working properly. Any thoughts on how to accomplish the same thing with df0: ("validate" isn't an AmigaDOS command)?