It may just need a drive letter assigning to it, without which Windows Explorer can't show it.
Go to Control Panel > Admin Tools > Computer Management > Disk Management
In the bottom-right panel, look for a drive ribbon on which it says "Raw" and has no drive letter.
Right-click on that and choose "Change Drive Letter & Paths"
Click "Add"
Accept the default letter or choose one and click 'OK'
Wait a few seconds until the drive description changes on the ribbon.