itunes music has vanished

[musicbaby]

hey
so, i turned on my itunes a minute ago and all my music, movies, podcasts are all gone and it looks like a new itunes library!
What is the cause and how can i rectify this?
Ive spend two years building up my music and im kinda freaking out!!

 

[Cinematographer]

I guess you already tried:

Restart iTunes.

Restart computer.

If that did not help: go to your home directory and find the music/iTunes folder. There should be at least a iTunes Library file, a iTunes Music Library.xml file and a folder with your music. Are the files still there?

Pleas report back and give more info: OS version, iTunes version.