|Laptop / desktop? IDE, SATA HDD?????|
Check to see if the WD HDD is listed in your BIOS 1st.
If it is, test the WD HDD with WD's DataLifeguard utility. Search for it on their site,
http://www.wdc.com/en/ , DataLifeguard versions are are drive specific.
My guess is that the drive or the drive electronics may have failed.
Just another stupid saying...