Have you maybe run SFC ? (system file checker?) did a disk check?
Yes, I did. After a lot of disk activity, it asked me to insert my original disk -- which I have NEVER had.
I then connected the Ethernet cable and re-ran SFC, but it found nothing on the Internet.
Finally, and this may or may not be related to the SFC search, a few days later my PC took MUCH longer than usual to boot, so I turned it off, took it apart, salvaged the hard drive, threw the metal parts on my scrap-metal pile, put the power supply and motherboard in my electronic-scrap "collection", discarded the miscellaneous parts that remained, and called it "quits" for my Vista computer!
I'll now go back to an old XP machine and see what happens.
Thanks again to everyone who tried to help me.