I am a new MAC user, and have never had any problems with my external hard drive until now. When I plug it into my Macbook Air via the USB port I receive the following message: 'The disc you inserted was not readable by this computer.' Does anybody have some advise on how to retrieve my files? I have tried reading other forums on this matter, but I am having a problem understanding the resolution. FYI - When I look in Disc Utility and highlight the ext. hard drive, the verify and repair disc options are greyed out and unable to be clicked Your assistance is appreciated. Thanks.