Basically, at this point I’ve given up trying to salvage this HD, due to the time and effort invested already, and I may not get any results. I didn’t even finish the HD diagnostic; only did the quick test and it’s showed several bad sectors. Removed the drive from the chassis, and want take a look at what files might be salvageable and recover what I can from it by putting it in an external drive. This PC was replaced last year, so I was getting it cleaned up to use for hooking up a security system and whole house audio, and would have wiped the drive anyway. This HD was the original primary drive, and was 6+ years old. They all fail at some point.
Thank you everyone who tried to help.