How is the My Book Essential encrytion work?

i have a WD My Book Essential 1.5T, i got many important files inside and lock with the WD locker. But the casing is damage and i have to replace a new casing but i cannot encryte the hard disc and their is no message pop up ask me to enter my password. So more when i check in my disk management, the disc is unallocate space. Izit mean i lose all my files??? hope i can get u anwer very soon.

You could have lost the files

try using a recovery software before reformatting