Western Digital external hard drive problem

I have a similar problem.  I have a lot of material saved on my WD portable HD (500 gb, usb cable only power source) and NOW no computer can access it.  It powers up (I can hear it running) the computer recognizes when it is plugged in and unplugged but it doesn’t show up in my windows explorer. 

I need to find a way to access the files.  I tried plugging it into different usb ports on my laptop and I also tried to access it from other computers.  I searched for it, but the HD isn’t showing up.

Can someone help me.