I have two wd 1.5tb external hard drives, and I want to transfer all the content on one to the other. The problem I am having is that when I go into my computer, only one hard drives shows up in G drive and not the other. I have 3 usb ports so why is this happening?
Please help!

Go into Computer management and assign a different letter to each drive.
Then it's a simply copy/paste exercise.

Make sure both hard drives are also plugged into power. Also plug them into USB ports on the computer itself and not a USB hub.

Have you already formatted and partitioned the drive that is not showing up? Sometimes this needs to be done (usually not, but it can happen that this is required).

What operating system are you using (Windows XP, Windows 7, Mac OSX, etc)? Are the hard drives exactly the same model as one another?

Thanks heaps for your help, I found that I was getting a conflict between the two drives as the format was the same. So in computer mamagement I found that one of the drives was off-line and all I had to do is switch it to on-line. Thank you again for your advice. Adios Ash

Thank you for you help, but I sus it out. Adios Ash.