PC won't recognize external hard drives

[dakinsfsu]

I’m a Windows 7 user. I have two WD 1TB hard drives and my computer will not recognize either of them. Upon plugging them in, the computer makes the typical sound recognizing something has just been plugged into the computer but no drive or device is recognized.

I’ve plugged other devices in to ensure it is not a problem with any of my USB drives at they all work without fail.

Help please.

[Trancer]

Welcome to the Community.

Are you able to specify the type of external hard drive you are trying to use? Is it a My Book Essential or a My Book Studio? Is this the first time you try to connect these hard drives to your system? have they worked before in other computers?