Just received my 2012 2.6GHz MBP with a Hitachi 750GB/7200rpm drive. Removed the HD and replaced with my Samsung 830/256GB from my Early 2011 MBP. Turned on the new MBP and got a grey screen with an icon showing a circle with a line through it. Put everything back in original order. Started the new MBP with the Hitachi and completed the setup. Again, turned off the new MBP and swapped the drives and same thing happened. Each time I swapped, I replaced the SSD in my previous MBP and started without any issues... So I haven't screwed up the SSD nor the new MBP with the Hitachi HD. Just can't get the new MBP to see the Samsung SSD. (BTW, holding down the opt. key with the new MBP and the Samsung SSD installed shows Macintosh HD, Windows 7 (bootcamp) and Recovery HD. I can boot into Win 7 - though keyboard/trackpad does not work so I have to hold down the power button to restart - but not Macintosh HD which is the Samsung SSD.) Any ideas? Thanks!