Godfrey DiGiorgi says:
The way Lightroom manages image files, catalog and previews is quite different from the way iTunes works ... don't draw any conclusions from your iTunes experience, they're not related to how Lightroom works.
The question is "how did you move your photos and catalog to the new computer?" Was it from Mac to Mac, Win to Win, Mac to Win, Win to Mac ... ? Did you move the whole catalog folder? Did you use the "Update Folder Location" command on the new system to tell Lightroom where your files are?
I have a document describing how to move a large number of files on my articles page: see www.gdgphoto.com/articles/ click on #08.
ASSUMING you have done the job correctly and the catalog knows where the image files are, it's probable that Lightroom has to regenerate all the previews in order to show you thumbnails. I've seen this happen particularly when moving cross-platform, but also occasionally when moving on just one platform. The way to do this is simple:
- Quit Lightroom
- In the catalog folder, delete the .LRDATA file.
Do not delete the .LRCAT file!
- Re-start Lightroom
LR will re-build all the previews this way from scratch. This may take some time, depending on how big an image collection you have.
Stu, I would recommend moving the files in Lightroom from the Mac onto an external drive (formatted as Fat32 that can be read by Mac and PC). Make sure all of the folders containing your images are in Top Level folder. Then copy your catalog folder onto the same external drive. Now you can just plug the external into the PC and copy the catalog folder across to the PC.
Next double click the .lrcat file to open Lightroom and the Catalog. As it is an Lr3 catalog it will be upgraded to an Lr4 Catalog. Then you will most likely need to relink the Top Level folder as the drive name will be different. If you want you can leave the images on the external or you can then use Lightroom to move them to the PC.