WD my book 3TB USB 3

my hard disk is unexpectedly disconnected … any one knows whats the problem 

im using MAC os 10.8.3 on Mac book pro 15 retina dispaly 

the hard disk format is MAC os extended (journaled, Encrypted)

Hi, as a troubleshooting step, try connecting the power cable directly to a wall socket. Connect the USB cable directly to the Mac and avoid using USB extension cables or USB hubs. To test the My Book use the Disk Utility app. Check the link below for the steps. 

How to test a drive for defects or problems on a Mac