Trying to delete some unnecessary files to make room on the hard drive (hoping this will help me boot so I don't have to reformat or replace the drive).
Yes, 500GB drive is full to capacity (19MB free).
Found another thread, started in Single-User mode, Mounted the drive in Read-Write mode ("mount -uw /" command), then was able to "rm" a bunch of files in the Downloads folder ... It seemed to be working, "ls" command, while in Single-User mode, revealed the files I removed were gone ... or so I thought.
Unfortunately, when I restarted in Recover mode, to attempt repair again, Disk Utility STILL says only 19MB on the drive and STILL will not repair. And, while most of my important files are backed up, I DON'T have a complete backup
If anyone has suggestions for attempting recovery of a drive full to capacity, please let me know. Otherwise, I think replacement and starting over - and losing some files along the way - is likely my next, painful step.