I bought a new hd for my macbook when i first got it. I had the original drive which i didn't use for a while, and recently got a housing for it to be external. It connects via USB and powers via usb no external adapter. It mounts as the original 'macintosh hd' because it has os x installed but when i try to reformatt it in disk utility i always get the same error, drive can not unmount. i can't even repair permissions.