Generally speaking, if you're going to reformat a hard drive you want to back-up all your files to an external location (external hard drive, Dropbox, Creative Cloud, that sort of thing) so that you can retrieve them later.
Assuming you did that and then retrieved them after the reformat but still can't locate them using Lightroom, I'm going to move this to the Lightroom forum in the hopes someone there can help you.
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Presumably, therefore, your images were on the external hard drive that was reformatted, in which case the images are no longer there (the "?" on the folder and sub-folders means that Lightroom can no longer find them). So they have to be restored from a backup, assuming you do have a backup? Do you have a backup, and if so where is it?