How to unlock my WD500H032

Yes I know its an OLD OLD drive!  But I recently found it and its pretty empty.  For some reason its locked and I can’t unlock it to add or remove things from it.  Does someone know how to do it.  I know on the back there is a a little lock icon on the serial bar sticker and an opening but I have no idea what to do to get it to unlock.  I have tried pushing something  but nothing budges and flicking a switch but nothing budges.

Help is greatly appreciated.  Thanks.!

The drive you mention does not come with encryption. That lock is to attach an extension and secure the device in the event of theft.

What message do you get when you try to transfer files to the drive?