I'm new and here's my issue: Multiple external disks (many of them new, and formatted for Mac) are mounting on the desktop, but with empty volumes. Volumes containing already recorded information are made invisible/inaccessible, even with Disk Utility. Data Recovery programs recognize raw data, but much of it comes back scrambled or unopenable. What is happening? Has this happened to someone else? Is it my computer, or is it the disks? About the computer: 2009 Macbook Pro. I have two separate internal disks with two separate operating systems, one is OSX Leopard on a HDD, one with OSX Yosemite on a SSD. I boot from one or the other, depending on the software I want to use. the HDD is now having problems and suggests I back up my files and reformat ASAP. The SSD still works fine. About the external drives: One is a G-technology 1tb drive, the others are WD 4TB drives. They've worked fine for a couple plug-and-plays, and then one day suddenly they will stop mounting the volumes to which I've saved information, showing new, empty volumes with greyed-out folders by the names [see pic]. Any help would be appreciated.