Yea, you guys can imagine what happened to me when Windows recently crashed on my Media PC... to the point I had to use external media to completely re-install Windows 10. All my settings were changed, JRiver had to be restored, and then when first went back into JRiver, my library was all screwed, no playlists etc. It was a mess.
Part of what happened to me, Windows managed to change drive letters on multiple drives... and my Library was trying to import items from the new locations. After a few pints and 4 letter words, what finally worked for me was going back into Disk Management, putting drive letters back to my old configuration, making sure folders were the same and in the original locations from a month ago... then went to my Cloud backup (luckily I had one) and restored my previous month Library backup and voila... it worked. All my playlists were back, media was fine and movies there ready to go.
Just wanted to share in case someone else faces this challenge. I am technically savvy, just enough to cause trouble but it felt great to get back up and running. And I poured another pint!!!