I just ran into this problem again, I have one of the 500 Gb drives not used and formatted that I put into the computer and it did not show up in Explorer, I tried formatting it in computer management, it came out as a master boot and still did not show up in Explorer. I just tried computer management again, I made a simple volume and this time assigned a drive letter to it labeling it storage. It is now visible and available for storage.
Carl2