Formatting a WD hard drive

I bought a WD hard drive back in October to back up my macbook pro on it and I haven't used it since. I recently tried to connect it back in my laptop to back it up again. As soon as I plugged it in it asked for a password. I forgot the password so I said i’ll try again the next day. I plugged it in the next day and it did not show up on my mac. I searched many ways to try to make it show and nothing worked. It is still not showing anywhere on my mac. How do you think I should proceed?