My Book Essentials 3 TB is READ ONLY!

I need help and it seems this may be the right thread. My WD Essential drive has been used for my Time Machine Backup drive for the past year. 1TB and not even close to being full and I was able to access files on the disk and all was working fine. Until about a week ago when i started receiving a Time Machine Backup error stating the drive was “Read Only”. Now it won’t even show the disk. What can I do? Thanks in advance for the help.