I have a 3TB Western Digital (My Book Studio or something like that) external hard drive, which I had used with my 27" iMac that I sold, and now with my mid 2010 Mac Pro. The weird thing is, when I turn off the Mac, but the HD is still connected, the light is still blinking. I'd understand if it was when the Mac is put to sleep - but when it's turned off? I never had this problem with the iMac. So I unplugged the Firewire cable from the Mac to the HD to see what would happen, and it stopped blinking. Another time that didn't work and so I had to remove the power cable from the HD. Anyone know why this is like that? Is the HD failing? Thanks a lot!