How do i transfer albums from my backup drive to itunes on my new PC?

OK then. My PC started to show signs of age, so i bought an external back up drive and copied everything to it. I have now copied my itunes albums from the back up into my itunes folder on my new PC. They are sitting in the same folder as the pre loaded windows stuff that Itunes has picked up. But my albums do not show on itunes. please help.