I wrote:
After I ran hwinfo (to detect a modem), my machine runs very slowly at the beginning of booting. (GRUB takes about 8 seconds between displaying [the] "Welcome to GRUB!" text and the "error: fd0 read error." text, and another 25 seconds for the screen to go blank on the way to displaying the menu. ...) What the heck did hwinfo do to my machine?
Thanks to some suggestions that somehow caused me to check basic floppy access, I discovered that the problem was ... (get ready for a big letdown) ... a loose floppy cable. (Apparently plugging in the modem--or, more likely, unplugging and re-plugging the motherboard-to-DB9 adapter cable to check something--jostled a incompletely seated floppy drive cable enough to disconnect some pins. Re-seating the floppy cable has restored the previous behavior--no major delays between the "Welcome to GRUB!" text and the "error: fd0 read error." text, or from there to the GRUB menu.) Thanks for the help. Daniel