Original post by: Dan ,
I would start off replacing the HD cable as they tend to breakdown. Here is the IFIXIT guide: [guide|5120|MacBook Pro 13" Unibody Early 2011 Hard Drive Cable Replacement] and this is the cable you want as it's the improved version: [product|IF163-041-2|MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable]. But before you do that visit any Apple Store as Apple has been replacing them for free for a lot of people. Put the original drive back in before you go. Let us know how it goes.