Hi! I am really stuck as to why my macbook pro will no boot from the main Sata bay. I have the macbook pro late 2011 - a few months ago I installed a samsung 840 evo, and moved the 500gb hdd into the optical bay and all has been working perfectly until last night. I installed yosemite two days ago and it worked perfectly to begin with... then when I re opened my laptop everything was frozen. I restarted it and it wouldnt get past the grey screen. Then I managed to get it to the internet recovery stage....however it would not recognise the SSD, so I had to install Lion on the HDD. After I logged on it gave me the message saying that the disc is not readable and on disk utility I can only see the "samsung ssd" but no details about it. I thought that the SSD may have gone, but when i removed it and plugged it in via USB I was able to boot from it with no issues. Does anyone know if this has anything to do with the new OS? or whether it is the Sata cable? Thanks for any help!!!