Maybe, filters are hiding your loops. Does your project have an unsual signature? For some signatures there are simply no loops available. Or do have enabled the Preference
Preferences > Loops > Keyword Browsing : Filter for more relevant results?
But if no filters are set, check the install locations for the loops: See this knowledge base article on how to find the install locations:
The bulk of loops should be in the system library: /Library/Audio/Apple Loops/Apple/
Check the permissions on these folders. If The loops are there, but GarageBand does not see them, repair the permissions using Disk Utility.
Then try to reindex the loops again:
It is very unusual, that you suddenly get prompted to rebuild the Loop index.
What happended, before this occured?
Did you install or upgrade any oter software? Run maintainance programs, that clean your Mac or something?
If you should find, that the loops are no longer where they are supposed to be, restore the loops folders from your Time Machine backup, or reinstall GarageBand and any JamPacks you are using.
I wrote a song on a Mac with iLife '09 and transported it to my current mac which runs iLife '11. I'm thinking Garageband put all of my loops on the flashdrive.
Have you any JamPacks installed on your Mac with iLife '09, that are not installed on your current mac?
Then many of your loops may be missing.
When you transfer a song between macs with different instruments, you can save the song as an archive, Then GarageBand will add the instrument samples to the projects, but as a copy, not the orignals.
You cannot download the loops separately.
I tried reinstalling garageband but the loops are still missing. Is there a way I can download them?
Most of the loops shuld be installed by the installer directly, and then you should be prompted to download more.
How did you reinstall? Download from the AppStore, or do you have an iLife installation disk?
Did the installer run without an error?
Do you have a Time Machine backup?
I tried reinstalling using the Appstore.
You ar saying "tried" - but with what success? Could you download GarageBand again and did the installer run?
If you could not reinstall, trash the GarageBand application - select GarageBand.app in the Appplications folder and press ⌘⌫.
You will be prompted for your Administrator password. Enter it. Don't empty the Trash.
Go to the App Store and sign into your account. Open the "Purchases" page. Reload it with ⌘R.
Now the GarageBand icon should show "Install".
Does that reinstall your loops?
The installation will/ should come in two stages - first basic contents, and when you launch GarageBand it will prompt you to download additional contents.
There may be a permissions problem with your system library and the loops folder.
I'd try to repair permissions with Disk Utility, and then again to reinstall:
For repairing permissions see: http://support.apple.com/kb/HT2963
It's not that the loops have faulty permissions. They are just totally missing.
And one possible reason, that reinstalling cannot restore them, might be, that the permissions in your system library may have become corrupted. Then the installer cannot write the loops to the folder where they should be.
Something must be preventing the installer from writing the loops to that folder.
That is why I suggested to repair the permissions on your Macintosh HD.
Do you see any error messages in the Console window, when you run the installer? (You can launch the Console.app from Applications > Utilities)
My loops have also disappeared, but as far as I know no "reindexing" has occurred.
I am not sure which Jam Packs are missing because the issue for me is that most of the Loops I created within GB, such as the 2013 copyright notice form my podcast, have dissappeared. Strangely enough I still have a few of my created loops, but all but three seem to have disappeared.