Cards, in the plural, I should say; so it is unlikely to be faulty cards. New Sandisk 64 GB SDXC from Amazon (so probably kosher). They appear to work fine in my D7200. Number of available image space is reported as 1.1k, and I can review recorded pictures. The Windows 7 computer cannot read the cards, and reports them as needing format (they were formatted in-camera). Everything still works fine with the old 32 GB cards. Is it possible that my card reader cannot handle 64 GB? I still use USB 2. Help appreciated.