I've had this 500GB external hard drive for ages (can't find which model it is? How do I find out? It doesn't have a power cable, just as USB cable) When I first switched from Windows to Mac, I formatted it as MS-DOS (FAT32) and it's been working fine. Then it stopped working. The green light comes on and stays on when it's plugged in. It shows up in Disk Utility as "not mounted". When I click "repair disk", it comes up with the following: Any help? I have most of it backed up so I could just reformat but I'd quite like to fix it & keep the data if possible. Thanks!