Wd My Book Essential 1.5 tb disk ghost

:cry: before from one day it had in 600gb  music and today suddenly the disk they is empty.that is to say the disk today they is in situation unallocated space, can explain to me him this, it worked only 20 days and afterwards I lost all my music thus simply.!

functional my they is windows 7.

and I had installed wd smart ware