Can't find my previous music purchases to download???

Hi,

This is a bit strange. I lost all of my songs due to a hard drive crash a few days ago. I am trying to re-download all of my previous music purchases I made from the iTunes store but not all of the purchases are showing up under my account. I click on 'Purchased' and only some of the songs I bought appear in the list. All of my previous purchases were made under the same account, too. So, I am completely baffled by this. Any ideas or suggestions?

Thanks.