My Mac Book Pro running OS X 10.6.8 doesn't mount my Seagate 2tb Free agent hard disk. It shows up in disk Utility but doesn't mount. I tried repairing it but it gives me the following error: Verify and Repair volume SEAGATE 2TB Checking Journaled HFS Plus volume. Invalid B-tree node size The volume could not be verified completely. Volume repair complete.Updating boot support partitions for the volume as required.Error: Disk Utility cant repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files. I don't have a back up and don't know how to back up files since it doesn't show the disk. What do i do?