Hello guys, I am at my wits end with this. I have decided to upgrade my 2011 MBP 13" to a SSD but for some obscure reason it doesn't detect anything with SATA III. The original HDD works. An old SATA II SSD I had laying around works, but all the SATA III drives I have tried fail to be detected internally but pop up and can be used when in an enclosure. Lion can be restored to the SATA II SSD but all attempts to upgrade to sierra(or el capitan) just end up stalling. I don't know what to try next at this point.