This can happen for a variety of reasons, most of which are probably unknown.

You may find this first when trying to change file permissions on the folder structure, or when you cannot access the 'New' menu on right clicking

Try these steps:

1. Log on to the computer in question as an Administrator
2. Open command prompt as an Administrator
3. Open diskpart

4. Enter command list disk to show all disks

   DISKPART> list disk
   
     Disk ###  Status         Size     Free     Dyn  Gpt
     --------  -------------  -------  -------  ---  ---
     Disk 0    Online          953 GB  1024 KB        *

5. Enter command select disk n, where n is the number of the disk that is reporting as being write protected. It should then report Disk n is now the selected disk

DISKPART> select disk 0

Disk 0 is now the selected disk.

8. Enter command detail disk to view the disk details

DISKPART> detail disk

BIWIN SSD
Disk ID:

10. Look for Current Read-only state, it may, or may not, say 'Yes'. If it does say 'Yes', this can be changed by issuing the command attributes disk clear readonly
11. Then repeat the command detail disk to verify it has been cleared.
12. If it is not the case that the disk is set to read-only, it may be the volume that is set instead. In this case, first enter the command list volume

DISKPART> list volume

  Volume ###  Ltr  Label         Fs     Type
  ----------  ---  ------------  ----  ----------
  Volume 0     C   Windows      NTFS   Partition
  Volume 1     D   Data         NTFS   Partition
  Volume 2         SYSTEM       FAT32  Partition
  Volume 3                                       Partition

14. Now enter the command select volume n, where n is the volume of the disk that is reporting as being write-protected. It should then report Volume n is the selected volume

DISKPART> select volume 1

Volume 1 is now the selected volume.

16. Now enter the command detail volume to see if it is indeed write protected. Look for Read-only having a value of 'Yes'

DISKPART> detail volume

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
* Disk 0    Online          953 GB  1024 KB        *

Read-only              : No
Hidden                 : No
No Default Drive Letter: No
Shadow Copy            : No
Offline                : No
BitLocker Encrypted    : No
Installable            : Yes

Volume Capacity        :  700 GB
Volume Free Space      :  446 GB

18. To clear this it is a similar command as for the disk, this time it is attributes volume clear readonly
19. Finally, do another detail volume to verify it has been cleared
20. Once done, enter the command exit to close diskpart. You may now close the command prompt too