iTunes media gone after moving to new PC

Long story short, I was moving a clients "stuff" from an existing notebook PC to a different "newer" notebook PC. New Windows user profile for her on the "new" notebook (had already been used by another employee and already had iTunes on it).

Logged in to her new profile on the "new" notebook. Connected the SSD from the "old" notebook. Moved (should have copied) the "itunes" folder from the My Music folder on the old SSD to the My Music folder on the "new" notebook. Saw that it was a few hundred MB's in size as it was copying.

Started itunes (ver 11.something). All the albums popped up. Lots of them. Then, 5 seconds later, they were gone, except for one podcast. I looked in the iTunes media folder, no music files (except for podcast).

I couldn't believe my eyes! What could have happened to all the media? I'm not too worried for the user as she hadn't used the "old" notebook for more than a few weeks, so replacing the media shouldn't be a problem, but (more than anything) I'm curious where the heck the music could have gone, and why?!

Ideas, anyone?

Thanks!