My Mac crashed today and when it restarted, my external HD has failed. So, I went in to Disk Utility and was going to repair the disk, but none of the normal buttons such as "Repair Disk" were enabled. So, I went to Terminal and ran a few commands. It tells me that: diskutil repairDisk /dev/disk2 Unable to repair this whole disk: A GUID Partition Table (GPT) partitioning scheme is required (-69773) So, I plugged the drive in to my Windows computer and navigated to the drive (I have Mac Drive installed which allows windows to read Mac drives). The drive works fine and I can see all my files. Why is it that Windows can read all the files on my Mac Drive and yet Disk Utility can't even fix the partition? Anyway, what now? The drive is perfectly fine. It must just have a damaged partition. So, how can I repair the partition? Why doesn't disk utility want to deal with this?