Itunes is suddenly empty, itunes library still there on hard drive

When you need to restore your backed up iTunes Library from your external hard drive to your computer, follow these steps:

Quit iTunes.
Locate your external hard drive.
Mac: On the Desktop or Finder sidebar.
Windows: In My Computer

Drag the iTunes folder (backed up earlier) from your external hard drive to whatever location you desire on your internal hard drive. It is recommended that you choose the default location for the iTunes folder, which is:

Mac OS X: /Users/username/Music
Windows XP: \Documents and Settings\username\My Documents\My Music\
Windows Vista or Windows 7: \Users\username\My Music\
Open iTunes while holding down the Option key (Mac) or Shift key (Windows).

In the resulting dialog, click the Choose Library button.

Select the iTunes folder you just moved to the internal hard drive.
Click Choose.

Copy iTunes folder to your external hard drive
To copy all the items in your iTunes library (including the iTunes Library file that holds all your playlists, playcounts, ratings, and other data) to your external hard drive, follow these steps:

Quit iTunes.
Locate your external hard drive.
Mac: On the desktop or Finder sidebar.
Windows: In My Computer
Locate your iTunes folder:
By default, the iTunes folder is located in:
Mac OS X: /Users/username/Music
Windows XP: \Documents and Settings\username\My Documents\My Music\
Windows Vista or Windows 7: \Users\username\My Music\
If the iTunes folder is not in the default location listed above then you can find where the iTunes folder is located by following these instructions:

Open your iTunes Preferences:
Mac: Choose iTunes > Preferences.
Windows: Choose Edit > Preferences.
Click Advanced.
The location of your iTunes folder will be listed in iTunes Media folder location box, as pictured below.


Drag the iTunes folder to your external hard drive. This can take a while if you have a lot of items.


When the transfer is complete, your iTunes Library will have been successfully copied to your external hard drive.