My book I can't see it on my PC

WD External Drives External Drives for PC
8

Got it back!  Seems it was a flaky USB port.

I found instructions on the WD site that may be of use.  The link won’t paste in, so go to wdc.custhelp.com and search for

"A WD external drive is no longer given a Drive Letter by Windows (XP, Vista, ot 7), and data on the drive is inaccessible.

Good luck!