The Disk is Offline Because of Policy Set by an Administrator

 

1. Open Powershell as administrator

2. Enter get-disk

3. Note the number of the drive (2 in the example above)

4. Enter set-disk number -isoffline $false 

5. Enter get-disk again to check the status.

6. If the drive shows read-only follow this guide.

https://docs.microsoft.com/en-gb/archive/blogs/askcore/my-disk-is-read-only-help