My two External HD's vanished out of my editing Library in LR. I looked at my last backup and close to 13,000 pictures are in one file. How can I get all the pictures back into LR with their dates to work with them again? I think I may have had this happen because I was working in two External HD's? I have done this for quite some time and this is the first time I have had this happen. Yikes. Appreciate any suggestions.
Please show us a screen capture of what you see in Lightroom where the "vanished" external HD's should appear.
Also, it may be that you have accidentally opened the wrong catalog. Go to File->Open Recent and select each catalog shown there, do the "vanished" external HDs appear?
If something has "vanished" from a catalog, it is likely that you have multiple catalogs and are currently working in one that does not have images imported from the "missing" drive.