Thank you for your reply! Here is more info in response to your suggestions.
I obtained Fedora 27 from the following link, created a live image, and booted to it.
My bluetooth mouse initially did not work, but when I opened my computer to use the touchpad, the computer continued working, and I was able to boot to the Fedora 27 live image.
This establishes that Fedora 30 has not been configured to work with my computer. My computer is a 2008 Dell XPS M1730, with an Nvidia GeForce 8700M GT video card. Can Fedora 30 be configured to work with this computer? I’m puzzled why they didn’t design Fedora 30 work with all of the computers that the earlier versions of Fedora worked with. Note that Fedora 30 has the same problem with or without the external monitor connected.
My hard drives are SSDs, only a few years old. The Fedora SSD was new 3 years ago, purchased for installing Fedora. I can access the Fedora SSD when booted to Windows; I can see the directory structure and files on the drive; and I can copy any given file to my Windows drive and open it. I located the file grub.cfg and opened it on my Windows drive. It is readable, and, as far as I can tell, it is fine.
I subsequently rebooted to the Fedora 27 live image, and at the option window I hit escape to get the grub prompt. I then typed “linux rescue”. No info was displayed, and I eventually rebooted to the Fedora drive. The boot now worked, and I was back in Fedora 27. I tried a few things, and they all worked fine. I was pleased! But I rebooted to verify that I could reboot, and on the reboot, Fedora went into emergency mode. I then booted to the live image and did the rescue again. But when I rebooted to the Fedora drive, the boot went into emergency mode. It has been this way ever since. Thus, linux rescue worked the first time but not subsequently.
Per your suggestion, in emergency mode, I typed “systemctl --failed” and got the following line:
<97> systemd-fsck-root.service loaded failed failed File system check on /dev/disk/by-uuid/…
Per your suggestion, I then typed “journalctl -b -u systemd-fsck-root.service -xe” and got the following lines:
systemd: Starting file system check on /dev/disk/by-uuid/…
systemd-fsck: [the label shown to the left appeared on the LHS of each of the remaining lines]
Root contains a file system with errors, check forced
Root inode 395679 has an invalid extent node (blk 1606927, lblk 0)
Root: UNEXPECTED INCONSISTENCY; RUN fsck MANUALLY (i.e., without -a or -p option)
fsck failed with error code 4
Running request emergency.target/start/replace
systemd-fsck-root.service: Main process exited, code=exited, status=1/FAILURE
Failed to start file system check on /dev/disk/by-uuid/…
systemd-fsck-root.service: Unit entered failed state
systemd-fsck-root.service: Failed with result ‘exit code’
Do you understand the boot problem and how to fix it?
Do you understand why rescue worked the first time but not subsequently?