Some have had issues with a "Restore" via Time Machine and Logic.
Check to see if the samples are there:
Library:Application Support:Logic:EXS Factory Samples
Library:Application Support:GarageBand:Instrument Library:Sampler
If they are, you may need to rebuild the Spotlight Index:
System Preferences:Spotlight:Privacy Add the HD to the Privacy List, then remove it again (this will force an Index re-build)