Source: Windows Central When connecting a mechanical hard drive (HDD), solid-state drive (SSD), or an external USB hard drive to a computer, Windows 10 can usually detect and set it up automatically. However, sometimes, a newly added drive may not show up in File Explorer, which could indicate a number of problems. For instance, it could mean that there is a physical problem with the data or power connection. If the hard drive does not appear in File Explorer, this could indicate that the device is disabled, offline, or does not have a drive letter. You may be trying to connect a drive previously installed on another computer, the partition on the USB drive may be corrupted, or you could be dealing with a raw drive that was never configured. Therefore it was never initialized or formatted.