I've got a 2TB Seagate external desktop Backup Plus drive divided into three partitions (My backup, Wife's Backup, and a third for large files that need to be transferred between machines), all formatted as Mac OS Extended that I can no longer do anything with. A couple weeks ago one of My Backup refused to mount. Even in disk utility it won't mount. I tried running first aid on it - running Verify Disk says it needs to be repaired but running Repair Disk gives an error message that it can't repair the the disk. I went ahead and bought a new external drive for back up so I'm no longer concerned about any of the data on there. When I try to erase the partition that won't mount Disk Utility gives me an error message that it "Couldn't Open Disk". When I try to erase the disk it gives me an error on the other two partitions that it can't unmount. Same thing for when I try to repartition the drive. I've gone into Terminal and told it to force unmount the other two partitions but it still doesn't allow me to erase the disk. I also booted into recovery mode and tried disk utility from there but received the same error messages. On top of all of that I've tried these steps on several other Macs and get the same results. I also tried connecting it to a PC but I guess because the partitions are all formatted for Mac OS Extended none of them are recognized. Any ideas? I'd like to recover the drive and make it usable again but everything I've found through searching so far seems to not be working in my case.