you need to open regedit and do a search for StorageDevicePolicies.
If found, modify the key WriteProtect in the right pane to change it's value to 0.
If not found, navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\ , create a key named StorageDevicePolicies and then create a key WriteProtect in the right pane, give it a value of 0. Save and reboot.