My book essential not showing up at all please help

I was using this My Book Essential 3tb for a long time and no problem before. Today I tried to plug in the external hard drive into the computer to backup stuff. It didn’t show on my computer and I can’t access to the drive at all. I tried it unplug, remove turn off and I also tried on my laptop. And still nothing comes up. Are all my files in My Book are gone now? What should I do? Please help me.

What OS are you using and does the drive show in Disk Management?

Joe