Have you resolved the problem by now?
If not, tell us more.
Did you delete the complete folder /Library/Audio/Apple Loops/ or only its contents?
How did you uninstall and reinstall GarageBand? Did you move the GarageBand.app from the Applications folder to the Trash and then download the app again from the AppStore?
That should reinstall part of the Loop Library.
Or how did you do it exactly?
I'm also having this problem, however under different circumstances. Prior to my early 08 17" macbook pro failing completely, I figured I would copy over my copy of garageband, since I'd lost the install disk and didn't feel like buying it. I didn't copy over the loops and it was actually the hard disk I was using as a lifeboat for my files whilst fixing my old 'book that failed.
Anyway, go forwards a year and I'm back on my '08 instead of my mid '09 13" and thought 'Hey, let's buy the latest version!' so I COMPLETELY uninstalled the old version of garageband (loop folders and all), and eventually ended up installing it, it installed my loops and all was well. Unfortunately, it's broken again.
No loops. installing garageband on my 13" also has a thing about no loops.
I'll contact Apple support today and see what I can do. I'll keep you guys updated