Replying to Holy missing music! What?

I turn on my computer today. I have not synced my ipod i over a week, I have not updated to itunes 8, I have not touched anything in at least 4 days. I open itunes and I have no music. Purchases tunes, gone, illegal tunes, also gone, CD rips, toast. What exactly happened. Itunes help has been able to offer me no information, so I am searching the web for information regarding this problem. I do still have my ipod with all my music, even though last time I tried taking it off there I lost all my music, and I still have the limewire stuff from back in the day in a folder (I hope, I haven't checked yet) but I sorta wanna know what happened. Help?