I have been through 4 or more sessions with LR tech support people, in which they took me through at least 3 different procedures for connecting and re-connecting the folders and photos in Lightroom.  Each session lasted one or several hours, including sometimes long waits on the phone to reach the proper tech support person.  For one or two of those precedures, the tech support person and I put my computer to work on lengthy operation to make the connection with tens of thousands of files.  I would check from time to time to see how this was progressing.  Apparently the operation finished, and the computer crashed; then, on rebooting, most of the files were no longer seen in LR (but had not been lost on the storage system), and those that did appear on the "Library" screen had the "Photo is missing" sign. 

After two of those sessions with your people, things looked good in LR, and once I still had time to develop a photo or two.  But after booting my computer up the next day, the files all had the "Photo is missing" sign again.

As for drive letters, that's a mysterious situation, too.  The networked drive (Drobo system) where the images are stored is Z:, but somehow during the processes that your people have guided me through, a drive "X:" has appeared (displayed in black, not white) on the left panel of "Library." The X-drive also shows the folders but always with a question mark following each.

All this is very aggravating and a huge waste of time, of course.  I bought an expensive, high-powered computer specifically for using LR4 to process my thousands of photos -- and now it's not working out.

Please help me out.

Sincerely,

Ray