Hmm.
If you type regedit into the Cortana search field and press Enter to open the Registry Editor, do you see your Dell 518 listed at this location?
On the left pane expand the hives to this location:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\MountPoints2
On the left pane double-left-click on MountPoints2 to expand. If you see the Dell 518 listed as a sub-directory of the MountPoints2 hive, right-click on it and select Delete, then close Registry Editor, and restart computer.