Did you specify a folder to copy the files to?
Is it shown under the Folders tab?
Or are the thumbnails shown as a drive/device under the name of the memory card?
It could be that the photos were added rather than copied. If the card has been formatted the original images will have been wiped from the card. The only possibility is to recover the LR previews. You can download and install a utility from the attached link. A new script menu or icon will then appear on the menu bar to the right of Help. It should be possible to select the folder/drive and run the script to extract the jpeg previews although the size will depend on your preference settings.
In future it’s best to back up the images from the card or the new DNG copies before formatting the card in the camera.
The question mark on the images means that the images are missing from its location.
You can find the images on your computer if you had chosen Copy, Copy as DNG or Move operation while importing.
You may perform searches on your computer to find the images.
For reference on the previous location of the images :
> Make a right click on the images and choose Show in Explorer.
> It will reveal the previous location.
There is no folder specified, that I can tell, except "previous import". I scrolled through the rest of the photos I had in this catalog, and 800 of 812 photos have gone missing. Maybe my computer has a bug? I also tried to install the script to recover the previews, and got all the way to the last step, where it says to open the script menu...there is no script menu or anything resembling that on my screen.
I definitely copied the pictures when I imported them. Is there any way they're hidden somewhere else on my hard drive? I'm wondering if I should take my computer to the shop and see if there's another problem. All of the pictures I've exported are safe in their files, but their LR copies are gone. Unfortunately, I hadn't exported these particular pictures.
If you select one of the images in the Previous Import and go to the Metadata tab on the right you should be able to see which folder they are in.