Help please. I back up my MacBook via Time Machine to an external WD Passport. It has not backed up since 11/28/10. Time Machine says my back up disk is unavailable, however it is fully plugged in, with light indicator on, and it "hums" as though it is working. I've been in touch via email with WD customer support. They suggested running "Disk Utility" on it. I did that with the option "Repair Disk." It failed. Now Disk Utility is suggesting I back-up, format, and restore from the backup. I don't have any place to back up my Time Machine Backups, I'm thinking of just formatting and starting Time Machine anew. Also, the Disk Utility is asking me what format I want to format the disk in. MacOS Extended (journaled), Case Sensitive, Journaled and case-sensitive, MS-DOS (FAT), and Xfat. I'm venturing into a new frontier here, and would appreciate guidance. PS- I do have another identical external My Passport that I did a CCC clone on a few weeks ago. I've never restored from one of those before. Thanks.