I have my stock 5400 500GB Toshiba drive from my 2011 MBP. I want to format it to use as an external HD but when I plug it into my MBP via an external HD enclosure, it won't show up in Disk Utility. Is there a reason why? I'm using the enclosure or guts rather, from my Western Digital My Book. When I got my Samsung 830 SSD - I used the WD enclosure to hook up and copy the original HD's data so it worked with the SSD but its not showing up for the old HD, any thoughts?