Wd my passport ultra not recognised by mac book pro

Im currently using a macbookpro (retina 15 in 2014) os x el capitan version 10.11.6 and Ive had this wd my passport for a while but didnt really start using it until now since my computer is out of space. At first, I was just plugging it in and an icon would pop up on the desktop. I could click on it and it would open up in the finder and i could see when the last backup had occured. I noticed that it wasnt backing up tho because the last back up date didnt match with the last time i plugged in the drive. From what i believe the drive is set to automatically back up once i plug it in. So i went into the time machine and tried to just manually back up the files. I tried doing the back up but i kept getting a message saying it was unable to do so… also when i would try to exit out of this, it said it could potentially do something to the drive… Finally i just exited out the folder, ejected the drive and pulled it out of the computer. I tried plugging it back in but the icon that was showing once before was no longer popping up. the drive was spinning and the light was on tho. i even went on my disk utility but the drive wasnt even popping up on that. I really dont know much about this thing and its kind of confusing lol help please thanks

Hello, Vajoiner1

Maybe you should try contacting WD’s Technical Support about this.

To Contact WD for Technical Support
http://support.wdc.com/support/case.aspx?lang=en