Thank you, Pags. The check-sums are identical for both disks, so I must believe that they are accurate. That leaves the sound problem.
Before this, it "just worked." As it does on the laptop, and on this machine in Mint. There are two sound decoders in this machine, one on the mobo which feeds the speaker output, and the other on the Nvidia card, which feeds the HDMI port (only.) I never had a problem with this
before, but could there be some kind of interaction? (There is no sound or video on the TV, but I would not really expect video, since I
have run the nvidia-settings to have only one display.) I have always used the default sound--alsa--and every time I fooled with pulse-audio I wound up with no sound, so please don't suggest that!
Does anyone know if the sound should work from the LiveDVD? I will try that and report.