Have you tried looking at it from the DiskManagement MMC? There are multiple ways to start this tool- here is one. From file explorer - right click on 'This PC' - Choose 'Manage' - Under Storage choose 'Disk Management' You should see your C: drive listed here as well as any other disks in your system.
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If you see your flash disk, then you need to look and see if it is partitioned, formatted, and if there is a drive letter mapped. Be very careful with this tool as you could erase data if you make a mistake.:). Dave, thanks. There wasn't an item as you suggested under 'disk drives' - but after rebooting the notebook with the SD Card inserted, I can now see an SD Host Adaptor ('SDA Standard Compliant SD Host Controller'). However, when I look at 'This PC' (I am on Windows 10) via File Explorer, I still cannot see anything that looks like an SD drive listed.