Logic Pro sounds aren't playing back when stored on my external hard drive.

My computer started running low on space lately, so I planned on moving my Logic sound library to an external drive, since it's what takes up the most of my storage. Once I was finally able to download it and get it transferred over, I reopened Logic, but the instrument/sound files that were moved make no sound in playback. Any ideas on why this might be happening? Do they need to be downloaded to my computer's drive in order to make sound?