Missing folders



At launch all the folders in LR5 on my iMac hd are question-marked as missing, though I haven't been moving them around. I can view all the images and they respond in develop mode. When I locate them - on the EHD image library - the corresponding folders on the iMac empty: the folders are there but no images. Only on the EHD are there folders with images.

I'm a bit anxious about continueing with this procedure. So should I continue? If I did, could then export (copy) the folders/catalogue to the iMac hd? Clear procedural advice would be most appreciated. Thank you.