Preview problems - Lightroom database... corrupt?

[nemophoto]

Over the past month plus, I've been migrating all my primary programs and data to a new computer. (Old= Win 7 x64, New=Win 8.1 x64). PITA, but that's another story. My issue is this:

I maintain separate databases for my images. For instance, each commercial job has it's own, which stays with the drive it's archived on. All my travel images are in another database, my Ireland images from my book in yet another, and all my various portfolio images in another. One reason is I hate the idea of all images residing in one lone, massive database... for exactly the reason I'm about to mention. All the databases I use regularly, open fine on my new system EXCEPT one of the most crucial -- my portfolio images. I tried opening the database. It shows that there are images, including the folders that contain the various images, but ONLY displays gray boxes -- NO images. I finally tried opening the database backup, and it displayed the images properly. There is a slight size difference between the backup and the primary, but I believe everything is there -- the system dates were the same from the last time I opened them.

So, these are my questions:
Why won't Lightroom display previews, even though the previews exist? It doesn't even try to regenerate them.
Why does the backup not contain the flags and color codes that existed with the original database? Any way to retrieve them?
Is the best way to use the backup, rename the original database, something like "OLD", then copy the backup into the folder where the original resided?
Is there anyway, still, to recover the original, since it supposedly has the flagged and color coded files?

Thanks for the help.

Nemo

[Schewe]

Not for nothing, but grey previews in LR is usually due to a corrupted display profile...what's your calibration and profiling situation. Have you tried using a different profile? Most systems on Windows provides a default sRGB profile. You might try that and see if it brings the previews back...

[wolfnowl]

Yes. Jeff beat me to it, but the one time I had grayed-out previews I had a corrupted monitor profile.

Mike.

[digitaldog]

Grey or really odd looking previews, mostly on Windows systems. Don't know why it affects LR but not necessarily Photoshop and other ICC aware applications.

Curious what happens if you try to update all the previews by moving the Previews.lrdata file and making LR rebuild it (yes, that can take ages).

[kaelaria]

Just delete the previews and recreate.

[nemophoto]

Thanks everyone for your thoughts. Valid suggestions, but my real question is then, why are other LR databases not effected, and why was the backup not effected? I calibrate once a month using an i1Pro spectro and the excellent NEC Spectraview II software. (I have dual 24" NEC P241W monitors.) So, it doesn't matter which monitor I have LR on, same thing with the same database. Tonight, I'll recalibrate and see if it has an effect, but so far LR and that one database is the only thing effected, that I can tell. No issues with PS and my prints match the monitor, when viewed in my lightbox.

[kaelaria]

Catalog.  And previews have nothing to do with catalogs.  Just delete them all and let them rebuild, it's not a big deal.

[digitaldog]

Thanks everyone for your thoughts. Valid suggestions, but my real question is then, why are other LR databases not effected, and why was the backup not effected?

Again, specifically this is the file you want to rebuild: Previews.lrdata file
Just move it outside the existing folder and let LR try to rebuild them. If that works, trash the original.

[nemophoto]

Thanks Andrew. I'll try rebuilding the previews over the weekend.

[nemophoto]

Success. I honestly didn't know I could delete (or in this case, rename) the preview folder and Lightroom would automatically rebuild. So back up and running. Thanks for the help... as simple a solution as it ended up.