Usually, when your external hard drive shows the "Drive is not accessible. Access is denied" error message, it is because you don't have the right privilege settings in Windows. So, to fix the issue, you have to take ownership of the drive. Here's how to do it:
Right-click on the inaccessible hard drive, select Properties. Go to the Security tab, hit Advanced, then click the Edit button. On the Owner tab, modify the ownership of the specified account.
Here is a thread as well that discusses the same issue and you can try out some troubleshooting steps from this and see if that helps you to sort the Issue.
SSD drive one partition not accessible
https://answers.microsoft.com/en-us/windows/forum/all/ssd-drive-one-partion-not-accessible/81bd8bef-6bb0-4e89-b21e-736c15b84564
Hope this resolves your Query!!
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