Why does Western Digital Smartware not detect my external HDD?

Why does Western Digital Smartware not detect my external HDD?

I recently buy WD Mybook Essential HDD 1 TB. I downloaded and install Smartware software in both my desktop (Windows XP) and laptop (Windows 7) but in both case the software is not able to detect the external hard disc. It shows desktop/laptop (Whichever is apt) on left hand side of software but not the hard drive on right side. Why so?