You can fix the inaccessible drive by adding an authenticated user or by taking ownership of the drive.
You can also use the CHKDSK Command to sort this issue.
- Open the CMD as admin.
-Enter the following command: chkdsk e: /f /r /x. ("e" means the drive letter of the partition you want to repair) - After the process, shut down the window. Try to access the drive again.
Below threads discusses the same issue and you can try out some troubleshooting steps from this and see if that helps you to sort the Issue.
The mounted backup volume is inaccessible
https://social.technet.microsoft.com/Forums/ie/en-US/97d2aa31-6e8e-4543-b85a-568837de7a9f/the-mounted-backup-volume-is-inaccessible?forum=windowsbackup
Hope this resolves your Query!!
--
--If the reply is helpful, please Upvote and Accept it as an answer–