@Preecha > Well, you're in a dilly of a pickle because while you can recover your music from the USB device, chances are it's not going to be in the same folder structure as you had previously, nor will you have any of the memory / cue points if your internal database was lost.
On your USB drive, go to the CONTENTS folder and you'll see all the music. Simply copy it from there back to your primary music drive.
And in the future, use the backup utility or a drive backup service (such as Backblaze - works online in the background and costs less than $5/mo for unlimited storage).